Ceramic heater and manufacturing method of ceramic heater

ABSTRACT

A ceramic heater manufacturing method capable of preventing reflection of a laser beam at the time the performing trimming by irradiation using a laser beam and performing trimming of a resistance heating element or a conductor layer. The ceramic heater manufacturing method includes forming a resistance heating element having a pattern on a surface of a ceramic substrate; and irradiating a laser beam onto the resistance heating element to form a gutter or a cut after a preceding step to adjust a resistance value of the resistance element. When the resistance heating element is formed on the surface of the ceramic substrate, the resistance heating element is adjusted to have a surface roughness Ra of 0.01 μm or more in accordance with MS B 0601.

TECHNICAL FIELD

The present invention relates to a ceramic heater to be used mainly forproduction or examination of semiconductors in semiconductor industriesand a manufacturing method of the ceramic heater.

BACKGROUND ART

Products for which a semiconductor is applied are very importantproducts necessary for a variety of industries and a semiconductor chip,one of the most typical products among them is, for example, produced byslicing a single crystal silicon into a given thickness to manufacture asilicon wafer, and then forming various circuits thereon.

To form a variety of such circuits and the like, it is required to carryout steps of applying a photosensitive resin to a silicon wafer,exposing and developing the resin, and then subjecting the resultingresin to post curing treatment or to sputtering treatment to form aconductor layer. For these steps, the silicon wafer is required to beheated.

As such a kind of a heater for heating a semiconductor wafer such as asilicon wafer used in the condition of setting the semiconductor waferthereon, conventionally those equipped with resistance heating elementssuch as electric resistors on the bottom face side of a substratecomprising aluminum are employed most, however the substrate comprisingaluminum has a thickness of about 15 mm and therefore is heavy and bulkyand not necessarily easy to be handled and insufficient in temperaturecontrollability in terms of the temperature-following property to theelectric current application to make even heating of a semiconductorwafer difficult.

In the publication of JP Kokai Hei 11-40330, there is disclosed aceramic heater composed of a substrate of nitride ceramics or carbideceramics with a high thermal conductivity and strength and heatingelements formed by sintering a metal particle on the surface of aplate-like body (a ceramic substrate) comprising these ceramics.

Further, as for a heater to be employed for such a semiconductorproducing device, the surface of the resistance heating elements thereofis easy to be affected by light and heat, treatment gases and the likewhen it is used as the semiconductor producing device, thus theresistance heating elements are required to have durability to oxidationon the surface.

Therefore, the inventors of the present invention have madeinvestigations aiming to form a resistance heating element excellent indurability and consequently found that formation of an insulatingcovering on the resistance heating element formed on a ceramic substratemakes a ceramic heater excellent in durability, for example,anti-oxidation property and the like. However, the insulating coveringmay work also as a heat insulator for the resistance heating element, sothat at the time of cooling after the ceramic heater is heated, quickcooling sometimes becomes impossible.

Further, as a method for forming the resistance heating element at thetime of manufacture of such a ceramic heater, conventionally, thefollowing methods have been employed; a method for forming theresistance heating element by a coating process such as screen printing;a method for forming the resistance heating element by a physicaldeposition method such as sputtering and a plating method afterproducing a ceramic substrate with a given shape.

In the case of a method for forming the resistance heating element usinga coating method after producing a ceramic substrate with a given shape,a conductor containing paste layer in a heating element pattern isformed and successively heating and firing is performed to form theresistance heating element.

However, although the resistance heating element can be formed at arelatively low cost, such methods have a problem that the resistanceheating element with a precise pattern can not be formed easily sincetrifling mistakes at the time of printing result in short-circuit in thecase of producing a precise pattern. The above-mentioned method hasanother problem that the printing thickness is not even andsubsequently, the resistivity becomes uneven.

Further, in the case of a method for forming the resistance heatingelement using a physical deposition method such as a sputtering and aplating method, after producing a ceramic substrate with a given shape,a metal layer is formed in a given area of the ceramic substrate bythese methods and successively etching resist is formed so as to coverthe portions on heating element patterns and then etching treatment isperformed to form the resistance heating element in the given patterns,or at first the portions other than the heating element patterns arecovered with resin and the like and then the above-mentioned treatmentis carried out to form the resistance heating element in the givenpatterns on the surface of the ceramic substrate by one time treatment.

However, although this sputtering or the plating method and the like iscapable of forming precise patterns, the method has a problem thatetching resist or plating resist has to be formed on the ceramicsubstrate surface by a photolithographic technique in order to form theresistance heating element with given patterns, resulting in high cost.

As a method for solving these problems, a method has been employed whichhas an advantage that precise resistance heating element patterns can beformed at a relatively low cost, that is: a method comprising steps offorming a conductor layer in a strip-shaped or a ring-shaped with agiven width and then removing the portions other than the heatingelement patterns using a laser beam irradiating equipment and the liketo form precise heating element patterns; or a method including thesteps of forming the resistance heating element by the above-mentionedmethod and successively irradiating laser beam to adjust the thicknessof the resistance heating element or to remove some portion of theresistance heating element so as to precisely adjust the resistantvalue.

However, by a conventional screen printing and the like, the surface ofthe resistance heating element or the conductor layer is smooth and atthe time of performing trimming by laser beam irradiation, in somecases, the laser beam is reflected at the surface of the resistanceheating element. Consequently, it becomes impossible to perform trimmingthe resistance heating element or the conductor layer as designed,resulting in unevenness of the depth and the width.

SUMMARY OF THE INVENTION

Inventors of the present invention have made investigations for solvingthe problem that a ceramic heater cannot be cooled quickly and foundthat adjustment of the surface roughness of an insulating coveringallows the insulating covering to function just like a heat releasingfin and thus drops the temperature of the resistance heating element atthe time of cooling, as a result, quick temperature drop of the ceramicheater became possible, and completed the first aspect of the presentinvention.

A ceramic heater of the first aspect of the present invention is aceramic heater comprising: a ceramic substrate; a resistance heatingelement, which is composed of one circuit or more circuits, disposed ona surface of a ceramic substrate; and an insulating covering provided onthe resistance heating element, wherein said insulating covering has asurface roughness Ra of 0.01 to 10 μm, preferably 0.03 to 5 μm inaccordance with JIS B 0601.

In the above-mentioned ceramic heater, since the surface roughness Ra ofthe surface of the above-mentioned insulating covering according to JISB 0601 is adjusted at a range of 0.01 to 10 μm, the insulating coveringfunctions to keep the temperature of the resistance heating element tosome extent and at the same time if there exists a coolant in thesurrounding, the roughened face formed on the insulating coveringsurface works as a heat releasing fin to carry out cooling at arelatively high speed.

Accordingly, at the time of raising the temperature of the ceramicheater, the temperature can be raised quickly and on the other hand, atthe time of cooling after the temperature rise of the ceramic heater,the temperature of the resistance heating element can be dropped quicklyand as a result, the ceramic heater can be cooled quickly.

Further, by adjustment of the surface roughness Ra of the insulatingcovering surface at a range of 0.03 to 5 μm, dispersion of thetemperature rise speed can be made small.

Further, since the insulating covering is formed on the surface of theresistance heating element in stead of forming a metal covering byplating and the like, at the time of application of electric power ofabout 30 to 300 V to the resistance heating element, the inconveniencethat electric current undesirably flows mainly at the surface of theresistance heating element does not take place, and the insulatingcovering can protect the resistance heating element. Further, even ifthe surface temperature of the resistance heating element is raised byelectric power application, since the resistance heating element iscovered with the insulating covering, oxidation or sulfurization byoxygen and SO_(X) and the like in air scarcely proceeds and change ofthe resistance of the resistance heating element can be prevented.

The reason why electric current flows easily in a plated portion in thecase the resistance heating element is covered by plating is that thereis a difference between: the resistance of the resistance heatingelement; and the resistance of the plated portion and in such a case,the resistance value of the resistance heating element is required to besmall. However, in the case that the resistance heating element iscovered with the insulating covering, since the covering is aninsulator, no electric current flows in the covered portion and thus,the resistance value of the resistance heating element can be set highand accordingly the calorific value can be designed to be high; or thecross-section of the resistance heating element can be made small toobtain the same heat calorific value.

If the surface roughness Ra of the above-mentioned insulating coveringsurface is less than 0.01 μm, the heat releasing function of theinsulating covering deteriorates, so that the cooling speed is retardedat the time of cooling the ceramic heater and on the other hand, if thesurface roughness Ra of the above-mentioned insulating covering surfaceexceeds 10 μm, air easily stagnates in the valley parts of the roughenedsurface, so that the cooling speed is retarded. In order to obtain theinsulating covering provided with both of such heat insulating effectand heat releasing effect, the surface roughness Ra of theabove-mentioned insulating covering is preferably 0.03 to 5 μm. This isbecause dispersion of the temperature rise speed becomes small. If Ra isless than 0.03 μm, heat reflection is high at the interface between theinsulating covering and air and on the contrary, if Ra exceeds 5 μm, theeffect of the heat release becomes significant to result in dispersionof the temperature rise speed. Incidentally, Ra is calculated bydividing the integrated value of absolute value of the surface roughnesscurve by the measured length, whereas Rmax is the height differencebetween a mountain part and a valley part in the curve of the surfaceroughness and both have no mutual correlation.

In the case the above-mentioned insulating covering is formed in astretch of area containing a portion on which the circuits are formed soas to cover the resistance heating element comprising, especially two ormore circuits, in a lump, the above-mentioned effects are provided andbesides, occurrence of short-circuit and the like in the resistanceheating element owing to the migration of a metal (for example, silverand the like) constituting the resistance heating element can beprevented. Further, also in the case of forming the insulating coveringin the above-mentioned areas, the covering layer can easily be formed byscreen printing and the like in the entire area including the portionswhere the above-mentioned circuits are formed, resulting in the decreaseof covering cost and cost down of the heater.

The ceramic substrate constituting the ceramic heater of the firstaspect of the present invention preferably comprises a nitride ceramicor a carbide ceramic. Because the nitride ceramic and the carbideceramic are excellent in the thermal conductivity for transmittinggenerated heat of the resistance heating element and excellent incorrosion resistance to a treatment gas in a semiconductor producingdevice and therefore suitable for a substrate for a heater.

In the ceramic heater of the first aspect of the present invention, theinsulating covering may comprise an oxide type glass. Because the oxidetype glass to be employed for these purposes has a high adhesionstrength to the ceramic substrate and to the resistance heating elementand is chemically stable and excellent in electric insulation property.

Further, in the ceramic heater of the first aspect of the presentinvention, the insulating covering can comprise a heat resistant resinmaterial. Because the heat resistant resin material usable for thesepurposes also has a high adhesion strength to the ceramic substrate andto the resistance heating element and is excellent in electricinsulation property and can be formed at a relatively low temperature.Incidentally, heating resistance means usability at 150° C. or more.

As the heat resistant resin material, one kind or more selected from apolyimide type resin and a silicone type resin can be selected.

Further in the ceramic heater of the first aspect of the presentinvention, a heating face is a side opposed to the side on which theresistance heating element is formed and a semiconductor wafer ispreferable to be heated on the heating face. It is because the heatgenerated by the resistance heating element is diffused while it istransmitted through the ceramic substrate, so that the temperaturedistribution similar to the resistance heating element patterns ishardly formed and a heat evenness property of the heating face can beassured.

The semiconductor wafer may be placed on the heating face. Also, throughholes or concave portions may be formed in the ceramic substrate surfaceand then, supporting pins may be installed in the through holes or theconcave portions so as to slightly project out of the ceramic substratesurface in order to hold the semiconductor wafer in the condition thatit is kept at 5 to 2000 μm from the heating face by the supporting pinsfor heating.

Incidentally, in the publication of JP Kokai Hei 6-13161, the structureof a ceramic substrate covered with resin is disclosed, however the ideadisclosed in the publication is that an object to be heated is put on aresistance heating element and thus, completely different from that ofthe present invention.

Further, Japanese Patent gazette No. 2724075 disclosed a method forcovering the surface of an aluminum nitride sintered body with a metallayer which is formed by: depositing an alkoxide, a metal powder, and aglass powder on the surface of the aluminum nitride sintered body; andfiring them. However, this patent relates to a package substrate and hasno description or implication that: the metal layer is a resistanceheating element; the opposite side of the face on which the resistanceheating element is formed is used as the heating face; and theinsulating covering is formed on the resistance heating element.Therefore, the novelty and unobviousness of the present invention cannotbe denied.

The ceramic heater of the first aspect of the present invention maycomprise a cooling device. The cooling device includes air-coolingdevice or water-cooling device and the like which are using a coolant.The heat exchange may be carried out: by conducting direct blowing ofthe coolant to the ceramic substrate; or by laying a cooling pipe in theinside of the device or the ceramic substrate.

As the coolant, gases such as air, nitrogen, argon, helium, and carbondioxide can be used and other than these, liquids such as water,ammonia, ethylene glycol and the like are also usable.

The ceramic heater of the first aspect of the present invention hassimilar effects even in the case of carrying out the cooling.

Further, inventors of the present invention have enthusiastically madeinvestigations for solving the problem that the resistance heatingelement or the conductor layer cannot be trimmed as designed at the timeof performing trimming using laser beam in the ceramic heatermanufacture and consequently found that: in the condition that a surfaceroughness Ra of the resistance heating element or the conductor layer is0.01 μm or more in accordance with JIS B 0601 at the time of theformation of the resistance heating element or the conductor layer onthe surface of the ceramic substrate, the laser beam reflection can beprevented and accordingly the resistance heating element or theconductor layer can be trimmed almost as designed without unevenness,and finally completed the manufacturing method of the present invention.

That is, a manufacturing method of a ceramic heater of a second aspectof the present invention is a manufacturing method of a ceramic heatercomprising the steps of: forming a resistance heating element having agiven pattern on a surface of a ceramic substrate; and irradiating laserbeam on to the resistance heating element to form a gutter or a cutafter the preceding step so as to adjust a resistance value of theresistance heating element, wherein when the resistance heating elementis formed on the surface of the ceramic substrate, a surface roughnessRa of the resistance heating element is 0.01 μm or more in accordancewith JIS B 0601.

Further, a manufacturing method of a ceramic heater of a third aspect ofthe present invention is a manufacturing method of a ceramic heatercomprising the steps of: forming a strip-shaped or a ring-shapedconductor layer on a given area of a surface of a ceramic substrate; andirradiating laser beam onto the conductor layer to remove a part of theconductor layer by performing trimming after the preceding step so as toform a resistance heating element having a given pattern, wherein whenthe conductor layer is formed on the surface of the ceramic substrate, asurface roughness Ra of the conductor layer is 0.01 μm or more inaccordance with JIS B 0601.

In the manufacturing methods of the second and the third aspect of thepresent inventions, since the surface roughness Ra of the resistanceheating element or the conductor layer on the ceramic substrate surfaceaccording to JIS B 0601 is adjusted to be 0.01 μm or more, laser beamreflection can be prevented and thus the laser beam can be absorbed inthe resistance heating element or conductor layer and as a result, theresistance heating element or the conductor layer can be trimmed asdesigned.

If the surface roughness Ra of the resistance heating element or theconductor layer on the ceramic substrate surface according to JIS B 0601is less than 0.01 μm, laser beam is reflected, so that the energy isdiffused and gutters and cuts smaller than those designed are formed,and it results in too smaller resistance value of the resistance heatingelement than a designed value or formation of the resistance heatingelement in different patterns (width) from designed patterns. In orderto keep the laser beam absorption efficiency high, the surface roughnessof the above-mentioned conductor layer is preferably 0.1 to 10 μm.

Further, according to the manufacturing method of the ceramic heater ofthe second aspect of the present invention, since the resistance valueis adjusted using laser beam, the resistance value can precisely beadjusted with little unevenness of the depth and width within arelatively short time and consequently, the temperature of the face forheating a semiconductor wafer and the like (hereinafter, referred to aheating face) can be made even to make it possible to evenly heat anobject to be heated such as a semiconductor wafer.

Further, according to the manufacturing method of the ceramic heater ofthe third aspect of the present invention, resistance heating elementpatterns with little unevenness of the depth and width can be formedwithin a relatively short time and the manufacturing cost can be loweredand complicated and precise patterns can be formed.

Accordingly, the ceramic heater having such resistance heating elementpatterns is relatively economical, has complicated and precise patternsand is capable of keeping the temperature of the heating face preciselyeven.

A ceramic heater of a fourth aspect of the present invention is aceramic heater comprising a resistance heating element formed on asurface of a ceramic substrate, wherein a gutter or a cut is formed at apart of the resistance heating element, and the resistance heatingelement has a surface roughness Ra of 0.01 μm or more in accordance withJIS B 0601.

Since the ceramic heater has a high surface roughness of the resistanceheating element surface, the atmosphere gas can be stagnated, and thusair in the gutter or cuts of the resistance heating element is preventedfrom flowing, and consequently, formation of low temperature portionattributed to the cuts or gutters is suppressed. Accordingly, thetemperature evenness of the heating face can further be improved.

Even in the case laser trimming is performed, when low temperature spotsare formed owing to the cuts or gutters, the temperature distribution inthe heating face becomes wide even if the resistance value unevenness ismade small, however in the ceramic heater of the fourth aspect of thepresent invention, such a problem is solved by making the surfaceroughness of the resistance heating element surface high.

If the surface roughness Ra of the resistance heating element surface isless than 0.01 μm, the atmosphere gas on the surface of the resistanceheating element flows, so that the effect to prevent low temperaturespot formation by the cuts or gutters cannot be achieved.

The resistance heating element is preferable to be covered by aninsulating layer. In the case a covering layer (glass or resin) isformed on the resistance heating element surface, in the case thesurface roughness of the resistance heating element is higher, thecracking by thermal impact is more difficult to take place.

Incidentally, in the manufacturing methods of the second and thirdaspect of the present inventions and the ceramic heater of the fourthaspect of the present invention, the surface roughness Ra of theresistance heating element surface is preferably 15 μm or less. Becauseif it exceeds 15 μm, unevenness of the width of the gutters or cutsincreases owing to the diffused reflection of a laser beam.

Further, if the surface roughness Ra of the resistance heating elementsurface exceeds 15 μm, the quantity of heat escaping to the atmospheregas from the resistance heating element surface increases, so that thetemperature distribution in the heating face becomes large.

Further, if the surface roughness of the resistance heating elementexceeds 15 μm, on the contrary, cracks are easy to be formed in thecovering layer owing to thermal impact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom plane view schematically showing one embodiment of aceramic heater according to the first aspect of the present invention.

FIG. 2 is an enlarged figure of a portion of the ceramic heaterillustrated in FIG. 1.

FIG. 3 is a bottom plane view schematically showing another embodimentof a ceramic heater according to the first aspect of the presentinvention.

FIG. 4 is an enlarged figure of a portion of the ceramic heaterillustrated in FIG. 3.

FIG. 5 is a bottom plane view schematically showing further anotherembodiment of a ceramic heater according to the first aspect of thepresent invention.

FIG. 6 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 1.

FIG. 7 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 2.

FIG. 8 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 3.

FIG. 9 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 4.

FIG. 10 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 5.

FIG. 11 is a block diagram schematically showing a laser trimmingequipment to be employed for the manufacturing method of ceramic heatersof a second and a third aspect of the present inventions.

FIG. 12 is an oblique view schematically showing gutters formed when aresistance heating element is subjected to trimming treatment.

FIG. 13 is a bottom plane view schematically showing one embodiment ofthe ceramic heaters according to the second and the third aspect of thepresent invention.

FIG. 14 is an enlarged figure of a portion of the ceramic heater shownin FIG. 13.

FIG. 15 is a plane view schematically showing other ceramic heatersmanufactured by the second and the third manufacturing methods of thepresent invention.

FIG. 16(a) to (d) is a cross-sectional view schematically showing aportion of manufacturing process of the ceramic heater of the second andthe third aspect of the present inventions.

FIG. 17 is a chart showing the surface roughness of the resistanceheating element surface formed on the ceramic heater according toExample 14.

FIG. 18 is a chart showing the surface roughness of the conductor layersurface formed on the ceramic substrate according to Example 15.

Explanation of Symbols  10, 20 a ceramic heater  11, 21 a ceramicsubstrate  11a, 21a a heating face  11b, 21b a bottom face  12, 22,(22a, 22b, 22c, 22d) a resistance heating element  13, 23 an externalterminal  14, 24 a bottomed hole  15, 25 a through hole  16 a lifter pin 17, 27 (27a, 27b, 27c, 27d) an insulating covering  19 a silicon wafer 110, 140 a ceramic heater  111, 141 a ceramic substrate  111a a heatingface  111b a bottom face  112 (112a to 112g), 142 (142a to 142d) aresistance heating element 1120 a metal covering layer 1130 a gutter 110 a laser trimming stage  110b a projection for fixation  110c astage  112m a conductor layer  114 a laser irradiating equipment  115 agalvanomirror  116 a motor  117 a control unit  118 a memory unit  119 acomputation unit  120 an input unit  121 a camera  133 an externalterminal  134, 44 a bottomed hole  135, 45 a through hole  136 a lifterpin  139 a silicon wafer

DETAILED DISCLOSURE OF THE INVENTION

At first, an embodiment of a ceramic heater of the first aspect of thepresent invention will be described with the reference of figures.

FIG. 1 is a bottom face view schematically showing one embodiment of aceramic heater of the present invention and FIG. 2 is a partiallyenlarged figure of the above-mentioned ceramic heater.

The ceramic heater 10 comprises a disk-like ceramic substrate 11 whichis made of an insulating nitride ceramic or carbide ceramic.Approximately linear resistance heating elements 12, for example, inconcentrically circular state as shown in FIG. 1, are formed on one mainface of the ceramic substrate 11; and the other main face (hereinafter,referred to as a heating face) 11 a is made to be a face for: putting anobject to be heated such as a silicon wafer 19 thereon; or holding theobject at a given distance from the heating face 11 a to heat theobject.

As illustrated in FIG. 2, through holes 15 are formed in the vicinity ofthe center of the ceramic substrate 11 and lifter pins 16 are insertedinto the through holes 15 to support the silicon wafer 19. Also, atbottom faces 11 b, bottomed holes 14 to insert a temperature measurementelement such as a thermocouple into are formed.

In this ceramic heater 10, as illustrated in FIG. 2, an insulatingcovering 17 with a given thickness and a surface roughness Ra of thesurface being 0.01 to 10 μm is formed on the surface part of theresistance heating element 12, so that the durability such as oxidationresistance, sulfurization resistance and the like is improved.Incidentally, in the ceramic heater 10, external terminals 13 areconnected to the terminal parts of the resistance heating element 12 andthe insulating covering 17 is formed also on a portion of the externalterminals 13. In such a case, generally, the insulating covering 17 isformed after the external terminals 13 are connected to the terminalparts of the resistance heating element 12.

In the case the insulating covering 17 is formed before connection ofthe external terminals 13, the insulating covering 17 cannot be formedat the portions where the external terminals 13 are connected.Accordingly, in such a case, the portions at which the externalterminals 13 are connected are generally not covered with the insulatingcovering 17. Accordingly, after the connection of the external terminals13, coating may be carried out again to form the insulating covering 17on the portions at which the external terminals 13 are connected.

Conventionally, in the case of a heater including a resistance heatingelement formed on the surface of a ceramic substrate, there is andisadvantageous point need to be improved such that heat is releasedfrom the exposed surface of the resistance heating element, andaccordingly the temperature of the heating face is not so raised for theapplied electric power, whereas in the present invention, since theinsulating covering 17 with a surface roughness Ra of 0.01 to 10 μm isformed, the heat diffusion from the resistance heating element 12 canappropriately be carried out.

That is, since the resistance heating element is covered with theinsulating covering having: the above-mentioned surface roughness; andproper thermal insulation effect, at the time of heating the ceramicsubstrate, heat is radiated at a high efficiency for the applied powerto keep a high surface temperature. Further, in the case a coolantexists in the surrounding, the roughened face formed on the insulatingcovering surface functions as a heat releasing fin, so that theresistance heating element can quickly be cooled and as a result, promptcooling of the ceramic heater can be achieved.

If the surface roughness Ra of the insulating covering surface is lessthan 0.01 μm, the thermal insulation effect is so significant thatefficient rise of the temperature is possible at the time of raising thetemperature of the ceramic substrate, however at the time of droppingthe temperature after heating of a silicon wafer and the like, thetemperature dropping speed of the resistance heating element is retardedand it is made impossible to repeat temperature rise and dropefficiently within a short time.

On the other hand, if the surface roughness Ra of the insulatingcovering surface exceeds 10 μm, air easily stagnates in valleys of theroughened surface and also since the thermal conductivity of theinsulating covering is low, the function as a heat insulation materialbecomes more significant than the effect as the heat releasing fin,making cooling efficiently within a short time impossible.

As the insulating covering 17, an oxide-based glass material or anelectrically insulating synthetic resin (hereinafter, referred to heatresistant resin) having thermal resistance such as polyimide type resinand silicone type resin can be employed. These materials may be usedalone or in combination (in layered form and the like) of two or morekinds of them. Incidentally, these materials will be described later.

Hereinafter, an instance of using aluminum nitride sintered bodysubstrate as a base material of the ceramic substrate is described,however the described base material is of course not limited to aluminumnitride and as the material examples, carbide ceramics, oxide ceramics,nitride ceramics other than aluminum nitride, and the like can beexemplified.

Examples of the above-mentioned carbide ceramics include, for example,metal carbide ceramics such as silicon carbide, zirconium carbide,titanium carbide, tantalum carbide, and tungsten carbide and the like,and examples of the above-mentioned oxide ceramics includes metal oxideceramics such as alumina, zirconia, cordielite, mullite and the like.Further, examples of the above-mentioned nitride ceramics include metalnitride ceramics such as aluminum nitride, silicon nitride, boronnitride, and titanium nitride and the like.

Among these ceramic materials, generally, nitride ceramics and carbideceramics have a higher thermal conductivity and therefore they are morepreferable than oxide ceramics. Incidentally, the materials of thesematerials for a sintered substrate may be used alone or in combinationwith two or more of them.

The ceramic heater comprising the nitride ceramics typically aluminumnitride and other carbide ceramics does not warp or strain by heatingeven if the thickness is thin because these ceramic materials have asmaller thermal expansion coefficient than that of a metal and alsobecause ceramic materials have high rigidity. Thus, the heater substratecan be made thinner and lighter by weight than that made of a metalmaterial such as aluminum and the like. Above all, since aluminumnitride is excellent in thermal conductivity, scarcely affected by lightand heat in a semiconductor producing device and excellent also incorrosion resistance to treatment gas, aluminum nitride can be employedpreferably as a heater material.

An insulating layer may be formed on the surface of the ceramicsubstrate comprising the above-mentioned nitride ceramics and carbideceramics.

That is because, in the case ceramic substrate itself has a highconductivity at a room temperature or a resistance thereof decreaseswhen the temperature thereof is in a high temperature region, if theresistance heating element is formed directly on the ceramic substratesurface, current leakage occurs between neighboring resistance heatingelement patterns and it results in incapability of functioning as aheater in some cases.

In this case, an insulating layer is to be formed on the ceramicsubstrate surface, then a resistance heating element is to be formed onthe insulating layer, and further an insulating covering is to be formedon the resistance heating element.

As the insulating layer, for example, an oxide ceramic is used. Such anoxide ceramic includes, for example, silica, alumina, mullite,cordielite, beryllia and the like. These oxide ceramics can be usedalone or in combination of two or more of them.

As a method for forming an insulating layer comprising these materials,for example, a method using a sol solution obtained by hydrolysis ofalkoxides, forming a covering layer by spin coating and the like andthen drying and firing the covering layer. Further, the insulating layermay be formed by CVD and sputtering and also the insulating layer can beformed by applying a glass powder paste and then firing the paste at 500to 1000° C.

The resistance heating element 12 is formed by forming a conductorcontaining paste layer in given patterns by applying a conductorcontaining paste containing metal particles of a noble metal (gold,silver, platinum, palladium), lead, tungsten, molybdenum, nickel and thelike and then sintering the metal particles by baking. The sintering ofthe metal particle is sufficient if the metal particles are fused to oneanother and the metal particles are stuck to the ceramic substrate.Incidentally, the resistance heating element 12 may be formed by usingconductive ceramic particles of tungsten carbide, molybdenum carbide andthe like.

At the time of forming the resistance heating element 12, the resistancevalue can variously be set by controlling the shape (the line width andthe thickness). Further, as being known well, if the width is adjustedto be narrower or the thickness is made thinner, the resistance valuecan be increased. The resistance heating element is in form ofapproximately linear or winding line with a certain width, however it isnot required to be strictly linear or winding from a geometric point ofview and may be in form of combination of straight lines and windinglines.

Since the oxide type glass material, which a material of the insulatingcovering, has a high electric insulation property itself as a materialand a high adhesion strength to the ceramic substrate and to theresistance heating element and is chemically stable, it can form astable interface to the ceramic substrate and interface to theresistance heating element.

Examples of its practical composition includes, for example,ZnO—B₂O₃—SiO₂ which is containing ZnO as a main component, PbO—SiO₂,PbO—B₂O₃—SiO₂, and PbO—ZnO—B₂O₃ which are containing PbO as a maincomponent. These oxide type glass materials may have crystallineportions. The glass transition point of the glass material is 400 to700° C. and the thermal expansion coefficient is 4 to 9 ppm/° C.

As a method for forming the insulating covering of such oxide type glassmaterials, a method for forming the insulating covering by applying apaste containing the above-mentioned oxide type glass powder to theceramic substrate surface by screen printing and drying and firing canbe exemplified. In this case, the portions where external terminals areformed are required to be covered with a layer of resin relatively easyto be decomposed at the time of heating so as to avoid the formation ofthe insulating covering.

At that time, the surface roughness of the insulating covering can beadjusted by changing the drying condition (drying speed), firingcondition (firing temperature), or the average particle diameter of theglass powder. Further, the surface roughening may be carried out byforming the insulating covering and then carrying out sand blasttreatment of the surface.

Further, a heat resistant resin material, which is a material for theinsulating covering, also has an excellent electric insulation propertyand a high adhesion strength to the ceramic substrate and to theresistance heating element. Further, use of the heat resistant resinmaterial makes formation of the insulating covering at a relatively lowtemperature possible. In the case of forming the insulating covering, itis only required to apply the material to the resistance heating elementsurface and dry and solidify the material, so that formation is easy andeconomical. Incidentally, the thermal resistance means that it can beused at a temperature of 150° C. or more and in such a case, nodeterioration of polymers and the like takes place.

Its practical examples include, for example, polyimide type resin,silicone type resin and the like. The polyimide type resin is polymercompounds obtained by the reaction of the carboxylic acid derivativesand diamines and has thermal resistance at 200° C. or more and can beused in a wide temperature range. Further, the silicone type resincomprises methyl and ethyl as an alkyl in the side chains ofpolysiloxanes and is excellent in thermal resistance and at the sametime has rubber elasticity, good adhesion property to the resistanceheating element and the ceramic substrate and is capable of forming theinsulating covering by being dried and solidified at a relatively lowtemperature, that is about 150 to 250° C.

As a method for forming an insulating covering comprising such a heatresistant resin material, a method comprising applying or spraying apaste containing the above-mentioned heat resistant resin materialdissolved in a solvent and the like to the ceramic substrate surface anddrying the material can be exemplified.

In this case, the surface roughness of the insulating layer can beadjusted by changing the drying condition (drying speed) and changingthe spraying condition and the like. Or, a roughened face may be formedby carrying out sand blast treatment of the surface or treatment using abelt sander after the formation of the insulating covering.

In this ceramic heater 10, the insulating covering 17 is formed on thesurface portion of the resistance heating element 12 and the thicknessof the insulating covering 17 is preferably 5 to 50 μm in the case ofthe oxide glass and 10 to 50 μm in the case of the heat resistant resin.

That is because, in the ceramic heater 10, cooling is required afterheating in order to turn it to a normal temperature and if the thicknessof the insulating covering 17 is too thick, cooling takes too long, andconsequently it results in productivity deterioration and on thecontrary, if it is too thin, the oxidation resistance of the resistanceheating element is lowered and the temperature of the heating face islowered attributed to heat release from the exposed resistance heatingelement surface.

As described above, if the insulating covering is formed on theresistance heating element surface, since these materials are excellentin the electric insulation property, it never occurs that electriccurrent leaks out of the insulating covering and flows and they canprotect the resistance heating element surface even in the case electricpower about 30 to 300 V is applied to the resistance heating element.

Further, the above-mentioned ceramic substrate has a high thermalconductivity and therefore can be formed to be thin in the thickness, sothat the surface temperature of the ceramic substrate can promptlyrespond to the temperature change of the resistance heating element andas a result, the ceramic heater 10 becomes excellent in temperaturecontrollability and the durability.

FIG. 3 is a bottom face view schematically showing another embodiment ofa ceramic heater of the present invention and FIG. 4 is a partiallyenlarged cross-sectional view of the above-mentioned ceramic heater.

The ceramic heater 20 comprises a plate-like ceramic substrate 21,similarly to the case of the ceramic heater 10 shown in FIG. 1. Theresistance heating elements 22 (22 a to 22 f) having approximatelylinear state concentrically as shown in FIG. 1 are formed on one mainface of the ceramic substrate 21 so as to form circuits; and the othermain face thereof is made to be a face to put an object to be heatedthereon or sustain it to heat the object.

Further, in the ceramic heater 20, the insulating coverings are formedon a stretch of area containing a portion on which the above-mentionedcircuits are formed. That is, around the resistance heating element 22a, 22 b, 22 c at which the circuits are kept at relatively widedistances from one another, the insulating covering 27 a, 27 b, 27 c areformed on a stretch of area containing a portion on which theabove-mentioned circuits are formed and the surroundings thereof, on theother hand, around the resistance heating elements 22 d, 22 e, 22 fwhich are kept at narrow gaps from one another, the insulating covering27 d is formed on the entire area comprising: the areas sandwichedbetween the neighboring resistance heating elements constituting thecircuits; their surrounding areas; and the areas between the respectiveneighboring circuits.

In the ceramic heater 20 with such a constitution, the same effect asthat of the case of the ceramic heater 10 shown in FIG. 1 is providedand occurrence of short-circuit between neighboring circuits owing tomigration of a metal particle (for example, silver particle) containedin the resistance heating element 22 can be prevented. Further, at thetime of forming the insulating covering 27, the insulating covering 27can be formed by forming a covering layer in a given area by screenprinting and the like and heating the covering layer, so that theinsulating covering can relatively easily and efficiently be formed andthe covering cost is lowered to result in an economical heater.

As the insulating covering 17 similar to the case of the ceramic heatershown in FIG. 1, either an oxide type glass material or heat resistantresin of such as polyimide type resin, silicone type resin can beemployed.

Further, similar to the case of the ceramic heater shown in FIG. 1, asthe material of the base material of the ceramic substrate, for example,carbide ceramics, oxide ceramics, nitride ceramics and the like can beemployed.

Also, for the material of the resistance heating element 22, similarmaterials to those in the case of the ceramic heater 10 shown in FIG. 1can be used and the resistance heating element 22 can be formed by asimilar method to that in the case of the ceramic heater 10 shown inFIG. 1.

In the ceramic heater 20, the thickness of the insulating covering 27(the thickness from the surface of the resistance heating element 22) ispreferably same as that in the case of the ceramic heater 10 shown inFIG. 1 and the thickness from the bottom face of the ceramic substrate21 at the portion where no resistance heating element 22 is formed ispreferably 10 to 50 μm in the case of oxide glass and 10 to 50 μm in thecase of heat resistant resin.

FIG. 5 is a bottom face figure schematically showing further anotherembodiment of the ceramic heater of the present invention.

The ceramic heater 30 has the same structure as that of the ceramicheater 20 except that an insulating covering 37 is formed in the entirearea where the resistance heating element 22 of the above-mentionedceramic heater 20 is formed and the same effect as that of the ceramicheater 10 shown in FIG. 1 is provided and besides, occurrence ofshort-circuit and the like in the resistance heating element owing tothe migration of a metal (for example, silver and the like) constitutingthe resistance heating element 22 can be prevented. Further, also in thecase of forming the insulating covering 37, it can easily andeffectively be formed because a coating layer is formed by screenprinting and the like and the insulating covering 37 is formed by aheating it and the like, to result in a decrease of a covering cost andcost down of the heater.

As described above, the insulating covering in the present invention mayinclude those having a variety of covering structures such as: thestructure of covering only on the surface of circuits; the structure ofcovering a stretch of area containing a portion on which the circuitsare formed: the structure of integrally covering two or more neighboringcircuits in the diameter direction of the ceramic substrate in a lump;the structure of covering the whole area where the circuits are formed;and the like.

Practical examples of the ceramic heater of the first aspect of thepresent invention with such a constitution and their manufacturingmethod will be described as the best mode for carrying out the presentinvention later. Of course, the practical examples and the manufacturingmethod to be described later are only examples and the ceramic heater ofthe first aspect of the present invention is not limited only to theseexamples and the manufacturing method at all.

Next, manufacturing methods of ceramic heaters of the second and thethird aspect of the present invention will be described.

The manufacturing method of a ceramic heater of the second aspect of thepresent invention is a ceramic heater manufacturing method comprisingthe steps of: forming a resistance heating element having a givenpattern on a surf ace of a ceramic substrate; and irradiating laser beamonto the resistance heating element to form a gutter or a cut after thepreceding step so as to adjust a resistance value of the resistanceheating element, wherein when the resistance heating element is formedon the surface of the ceramic substrate, a surface roughness Ra of theresistance heating element is 0.01 μm or more in accordance with JIS B0601.

The manufacturing method of a ceramic heater of the third aspect of thepresent invention is a ceramic heater manufacturing method comprisingthe steps of: forming a strip-shaped or a ring-shaped conductor layer ona given area of a surface of a ceramic substrate; and irradiating laserbeam onto the conductor layer to remove a part of the conductor layer byperforming trimming after the preceding step so as to form a resistanceheating element having a given pattern, wherein when the conductor layeris formed on the surface of the ceramic substrate, a surface roughnessRa of the conductor layer is 0.01 μm or more in accordance with JIS B0601.

There is a difference between both inventions: in the second aspect ofthe present invention, the resistance value of the resistance heatingelement is adjusted by performing trimming the resistance heatingelement formed in given patterns, whereas in the third aspect of thepresent invention, some portions of the above-mentioned conductor layerare removed by laser beam irradiation to form the resistance heatingelement patterns.

However, both inventions are in common in the point that laser beam isirradiated to a specified area of the ceramic substrate and theirradiated portions of the conductor layer (the resistance heatingelement) are removed and the same laser trimming equipment can beemployed.

Accordingly, hereinafter, except the cases separate descriptions arenecessary, the above-mentioned two inventions will be described inparallel.

At first, in the manufacturing methods of the second and the thirdaspect of the present inventions, the trimming method to be employed atthe time of performing laser trimming will be described and successivelythe laser trimming using the equipment will be described.

FIG. 11 is a block diagram showing the outline of the laser trimmingequipment to be employed for the manufacturing methods of the second andthe third aspect of the present inventions.

At the time of performing laser trimming, as shown in FIG. 11, a ceramicsubstrate 111 on which either a conductor layer 112 m is formed inconcentric circles (ring shapes) with a given width so as to include thecircuits of the resistance heating element to be formed or a resistanceheating element with given patterns are formed is fixed on a stage 110c.

On the stage 110 c, a motor or the like (not illustrated) is installedand is connected to a control unit 117 and the motor or the like isdriven by signals from the control unit 117 to make it possible tofreely move the stage 110 c in the θ direction (the turning direction ofthe ceramic substrate) and x-y directions.

On the other hand, above the stage 110 c, a galvanomirror 115 isinstalled and the angle of the galvanomirror 115 is made freelychangeable in the x-direction by the motor 116. The laser beam 122irradiated from a laser irradiating equipment 114 installed also abovethe stage 10 c comes into collision against the galvanomirror 115 andreflected thereon so as to irradiate the ceramic substrate 111.

Further, the motor 116 and the laser irradiating equipment 114 areconnected to the control unit 117 and by the signals from the controlunit 117, the motor 116 and the laser irradiating equipment 114 aredriven so as to turn the galvanomirror at a given angle around the axisin the x-direction. Also, a motor (not illustrated) installed in thestage 110 c is driven by signals from the control unit 117 to turn thetable in the θ-direction. Owing to the turning of the galvanomirroraround the axis in the x-direction and the turning of the table in theθ-direction, the irradiation position of the ceramic substrate 111 canfreely be set.

Incidentally, the table is able to turn not only in the θ-direction butalso move in the x-y direction.

In such a manner, the stage 110 c on which the ceramic substrate 111 isput and/or the galvanomirror 115 is moved, so that the laser beam 122can be irradiated to any optional position of the ceramic substrate 111.

On the other hand, a camera 121 is also installed above the stage 110 cand consequently, the position (x, y) of the ceramic substrate 111 ismade recognizable. The camera 121 is connected to a memory unit 118 andaccordingly the position (x, y) of the conductor layer 112 m of theceramic substrate 111 is recognized and laser beam 122 is irradiated tothe position.

Further, an input unit 120 is connected to the memory unit 118 andcomprises a keyboard (not illustrated) as a terminal and through thememory unit 118 and the keyboard and the like, given instructions areinputted.

Further, the laser trimming equipment is provided with a computationunit 119 and based on the data of such as the position of the ceramicsubstrate 111 recognized by the camera 121 and the thickness of theresistance heating element, computation for controlling the irradiationposition, the irradiation speed, the intensity of the laser beam 122 iscarried out and based on the computation results, instructions aretransmitted to the motor 116, laser irradiation equipment 114 and thelike from the control unit 117 to irradiate laser beam 122 while turningthe galvanomirror 115 or moving or turning the stage 110 c in order toperform trimming of the unnecessary portions of the conductor layer 112m.

Further, the laser trimming equipment comprises a resistivity measuringunit 123. The resistivity measuring unit 123 is provided with aplurality of tester pins 124. After dividing the resistance heatingelement into a plurality of sections, the tester pins 124 are broughtinto contact with the respective sections so as to measure theresistance value of the formed resistance heating element patterns.Then, based on the measured resistance value, laser is irradiated to thesections where the resistance value is low: to form gutters (referenceto FIG. 12) approximately parallel to the electric current flowdirection of the resistance heating element; or to form cutsapproximately perpendicular to the electric current flow direction, sothat the resistance value of the resistance heating element is adjustedand the resistance heating element with little unevenness of theresistance value can be obtained.

Next, a trimming method using such a laser trimming equipment will bedescribed specifically.

In this case, a method for forming a resistance heating element byremoving unnecessary portions of a strip-shaped or a ring shapedconductor layer which is formed on a ceramic substrate will mainly bedescribed and a method for adjusting the resistance value of theresistance heating element will be described later.

Further, the steps other than the laser trimming step in themanufacturing methods of the ceramic heaters of the second and the thirdaspect of the present invention will be described in details later andhere the steps will briefly described.

At first, a ceramic substrate is manufactured. In this process, firstly,a raw formed body comprising a ceramic powder and resin is produced.There are two production method of the raw formed body: one is aproduction method including the steps of producing a granule containingthe ceramic powder and the resin and then loading a die or the like withthe granule, and applying pressing pressure thereto; and the other is aproduction method including the steps of laminating and pressure-bondinggreen sheets. Proper methods will be selected depending on whetheranother conductor layer of electrostatic electrodes and the like will beformed in the inside or not and the like. After that, degreasing andfiring of the raw formed body is carried out to manufacture the ceramicsubstrate.

After that, through holes are formed in the ceramic substrate to insertlifter pins and bottomed holes are formed to bury temperaturemeasurement elements.

Next, to a wide area including the portions which is subjected to be theresistance heating elements on the ceramic substrate 111, a conductorcontaining paste layer with a shape as shown in FIG. 11 is formed byscreen printing and the like and after that, a conductor containingpaste layer is fired to form the conductor layer 112 m.

The conductor layer may be formed by employing a plating method, aphysical deposition method such as a sputtering. In the case of plating,a plating resist is formed and in the case of sputtering, selectiveetching is carried out, so that the conductor layer 112 m can be formedin the given area.

Further, the conductor layer may be formed as described above in amanner some portions of the conductor layer are formed as resistanceheating element patterns.

At the time of forming the conductor layer, the surface roughness Ra ofthe above-mentioned conductor layer according to JIS B 0601 is adjustedto 0.01 μm or more, preferably 0.1 to 10 μm. A method for forming aconductor layer (a resistance heating element) having such a roughenedface will be described in details later and in the case of forming theconductor layer by screen printing, the surface roughness of theconductor layer can be adjusted by selecting the shape and the averageparticle diameter of a metal particle to be employed as a raw materialfor the resistance heating element. Further, at the time of forming theconductor layer by plating, for example, if conditions under which anacicular crystal is precipitated is selected to carry out the plating,the surface roughness can be adjusted. Further, buff grinding, sandblast treatment is also capable of adjusting the surface roughness.

Next, as shown in FIG. 14, projections 110 b for fixation formed in thestage 110 c and to be brought into contact with side faces of theceramic substrate 111 and projections (not illustrated) for fitting tobe fit in through holes to insert lifter pins into are used to fix theceramic substrate 111 on the stage 110 c.

Further, data of the resistance heating element patterns is previouslyinputted through the input unit 120 and housed in the memory unit 118.That is, the data of the resistance heating element patterns to beformed by performing trimming is stored. The data of the resistanceheating element patterns is the data to be used for forming theresistance heating element patterns by performing trimming the conductorlayer printed like a plane (so-called spread state or ring shaped).

Next, the fixed ceramic substrate 111 is photographed by the camera 121,so that the formation position of the conductor layer 112 m is stored inthe memory unit 118.

Based on the data of the position of the conductor layer, computation iscarried out in the computation unit 119 and the results are stored inthe memory unit 118 as the control data.

After that, based on the computation results, the control signals aregenerated from the control unit 117 and while the motor 116 of thegalvanomirror 115 and/or the motor of the stage 110 c being driven, alaser beam is irradiated to trim unnecessary portions of the conductorlayer 112 m with the surface roughness of 0.01 μm or more and theresistance heating element 112 is formed.

At the time of removing the unnecessary portions of the conductor layerand the like in such a manner, it is important that even though theportions of the conductor layer and the like which should be trimmed bythe laser beam irradiation are trimmed, the laser beam does not affectthe ceramic substrate existing thereunder.

Accordingly, the laser beam is required to be selected so as to be wellabsorbed in the metal particle and the like constituting the conductorlayer and the like, on the other hand, be hardly absorbed in the ceramicsubstrate. Such laser type includes, YAG laser, carbonic acid gas laser,excimer (KrF) laser, UV (ultraviolet) laser and the like.

Among them, YAG laser and excimer (KrF) laser are the most optimum.

As YAG laser, SL 432H, SL 436G, SL 432GT, SL 411B and the likemanufactured by NEC can be employed.

As laser, pulsed beam with a frequency of 2 kHz or less is preferableand pulsed beam with a frequency of 1 kHz or less is more preferable. Itis because high energy can be irradiated to the resistance heatingelement within an extremely short time and the damage on the ceramicsubstrate can be suppressed to slight. Further, the energy of the firstpulse does not become high and gutters with a width as designed can beformed. If the frequency of the pulses of the laser beam exceeds 2 KHz,the energy of the first pulse becomes too high and the gutters with awider width than designed are formed and consequently, the resistanceheating element cannot be formed as designed.

Further, the processing speed is preferably 100 mm/second or less. It isbecause if it exceeds 100 mm/second, gutters cannot be formed unless thefrequency is increased. As described above, in order to limit thefrequency up to 2 kHz, the speed is preferably 100 mm/second or less.

The output of the laser is preferably 0.3 W or more. It is because if itis less than 0.3 W, the conductor layer to be removed for forming thepatterns of the resistance heating element may not completely trimmed insome cases. Especially, in the case the resistance heating element is ofa sintered body of a metal particle, trimming with the output of 0.3 Wor more can be carried out to the depth reaching the ceramic substrateand makes complete removal of the conductor layer possible.

Although trimming may be carried out for the conductor containing pastelayer, trimming is preferable to be performed after formation of theconductor layer, as described above, after printing a conductorcontaining paste and then firing the printed paste. It is because: theresistance value is fluctuated by firing the paste; and the paste maypossibly be peeled in some cases attributed to irradiation of the laserbeam.

The manufacturing method of the second and the third aspect of thepresent inventions is a method of forming a ring shaped (so-calledspread state) paste by using a conductor containing paste and performingtrimming the formed paste so as to pattern it. Hence, heating elementpatterns with an even thickness can be obtained. If the printing of theheating element patterns is conducted from the beginning, the thicknessbecomes uneven depending on the printing direction so that it becomesdifficult to form the resistance heating element with an even thickness.

In the above-mentioned description, the method for forming theresistance heating element by laser beam irradiation was described, butin the case of adjusting the resistance value of the resistance heatingelement by performing trimming after formation of the resistance heatingelement in the given patterns on the ceramic substrate, as shown in FIG.12, gutters 1130 are formed in approximately parallel to the directionof the electric current flow in the resistance heating element 112 andthereby, the resistance value of the resistance heating element can beadjusted. Although the resistance may be adjusted by forming cutsapproximately perpendicularly to the direction of the electric currentflow in the resistance heating element, the method for forming guttersis preferable since it is less probable to cause disconnection of theheating element.

In this case, as described above, the resistance heating element isdivided into a large number of the portions and using tester pins 124,the resistance values of the respectively divided portions are measuredand their resistance values are adjusted by performing trimming.

The patterns of the resistance heating element formed by such lasertrimming is not particularly limited and, for example, the followingresistance heating element patterns can be exemplified. Incidentally,hereinafter, the ceramic heater comprising the resistance heatingelement patterns will be shown.

FIG. 13 is a bottom face view schematically showing the ceramic heatermanufactured by the ceramic heater manufacturing method of the secondaspect of the present invention and FIG. 14 is a partially enlargedcross-sectional view of the ceramic heater. Incidentally, gutters formedby performing trimming are not shown in the resistance heating elementpatterns 112 a to 112 g shown in FIG. 14.

The ceramic heater 110 has the resistance heating element 112 (112 a to112 g) on the bottom face 111 b, the reverse side of the heating face111 a of the ceramic substrate 111 formed into a disk-like shape.

The resistance heating element 112 is formed into patterns composed ofbasically arcs so repeated as to draw a part of concentric circles inorder to carry out heating in a manner that the entire area of theheating face 111 a has an even temperature.

That is, the resistance heating element patterns 112 a to 112 d whichare closest to outer circumference are formed by repeating patterns inan arc-like shape formed by dividing respective concentric circles intofour and the end parts of the neighboring arcs are connected to eachother through winding lines to form series of circuits. Four circuitscomprising such resistance heating element patterns 112 a to 112 d arearranged near to one another so as to be surrounded by the outercircumference to form ring-shaped patterns as a whole.

Further, the end parts of the circuits composed of the resistanceheating element patterns 112 a to 112 d are formed in the inside of thering-shaped patterns in order to prevent formation of cooling spots andsubsequently, the end parts of the circuits in the outer side areextended toward the inside.

Inside of the resistance heating element patterns 112 a to 112 d formedin the periphery, the resistance heating element patterns 112 e, 112 f,and 112 g respectively composed of concentrically patterned circuits ofwhich slight portions are cut are formed and in the resistance heatingelement patterns 112 e, 112 f, and 112 g, end parts of the neighboringconcentric circles are connected to each other successively through theresistance heating element patterns of straight lines to form series ofcircuits.

Further, in the spaces between respectively neighboring resistanceheating element patterns 112 a to 112 d, 112 e, 112 f, and 112 g,belt-like (ring-shaped) no-resistance heating element formed area areformed and also in the center part, no-resistance heating element formedarea is formed.

Accordingly, as a whole view, the ring-shaped resistance heating elementformed area and no-resistance heating element formed area arealternately formed from the outer side to the inner side and inconsideration of the size (the diameter) and the thickness of theceramic substrate, these areas are properly designed, so that it is madepossible to make the temperature of the heating face even.

After trimming treatment, the resistance heating element patterns 112 ato 112 g are covered with a metal covering layer 1120 as illustrated inFIG. 14 in order to prevent corrosion and external terminals 133 areconnected to their end parts through the solder layer 1120.

In the ceramic substrate 111, three through holes 135 are formed at thepositions in the no-resistance heating element formed area and otherthan the case that an object to be heated, such as a silicon wafer 139,is heated while being put directly on the heating face 111 a of theceramic substrate 111, the object to be heated can be heated while beingkept at a given distance from the ceramic substrate 111 by insertinglifter pins 136 into these through holes 135 and holding the object tobe heated such as a silicon wafer 139 by the lifter pins 136 asillustrate in FIG. 14.

Further, it is also made possible to receive an object to be heated suchas the silicon wafer 139 from a transporting equipment, put the objecton the ceramic substrate 111, and to heat the object to be heated whilebeing supported. Concave portions are formed in the heating face 111 aof the ceramic substrate 111 and supporting pins are arranged in theconcave portions so as to be slightly projected out of the heating face111 a and the silicon wafer 139 can be heated while being kept at 5 to5,000 μm from the heating face of the silicon wafer 139 by supportingthe silicon wafer 139 by the supporting pins.

In the no-resistance heating element formed area on the bottom face 111b of the ceramic substrate 111, bottomed holes 134 are formed and in thebottomed holes 134, temperature measurement elements 137 such asthermocouples are inserted and it is made possible to measure thetemperature in the vicinity of the heating face 111 a of the ceramicsubstrate 111.

In the ceramic heater having the above-mentioned resistance heatingelement patterns, the resistance heating element is composed of: thepatterns forming series of circuits by combining arcs and winding linesrepeatedly formed as if drawing some portions of concentric circles onthe disk-like ceramic substrate (hereinafter, referred also to asarc-repeated patterns); and the patterns composed of series of circuitsformed by straightly connecting end parts of the neighboring concentriccircles of which small portions are cut (hereinafter referred also to asconcentric circles-like patterns), thus, most portions of suchresistance heating element patterns can be defined with distance r fromthe center of the ceramic substrate and the rotation angle (θ₁-θ₂).

Accordingly, at the time of performing laser trimming, if the ceramicsubstrate is mainly rotated around its center, the resistance value ofthe resistance heating element can relatively easily be adjusted and inthe ceramic heater comprising the resistance heating element whoseresistance value is adjusted by such a method, the temperature of theheating face becomes even and an object to be heated such as asemiconductor wafer can be heated at an even temperature.

Further, by the manufacturing method of the third aspect of the presentinvention, that is, by performing trimming of the conductor layer of theceramic heater formed in ring shape, the ceramic heater having theresistance heating element in patterns shown in FIG. 13 can bemanufactured. That is the same in the case of a ceramic heater havingthe resistance heating element with the shape described below.

The ceramic heater to be manufactured by the manufacturing method of thesecond and the third aspect of the present inventions is not limited tothose having the resistance heating element in patterns shown in FIG. 13and may have: the above-mentioned arc-repeated patterns; concentriccircles-like patterns and repeated pattern of winding lines, alone or incombination of these patterns arbitrarily.

FIG. 15 is a plane view schematically showing another embodiment of theceramic heater to be manufactured by the manufacturing methods of thesecond and the third aspect of the present inventions. In the ceramicheater, as shown in FIG. 15, resistance heating element patterns 142 a,142 b, 142 c mainly composed of winding lines and respectively formed ina ring shapes are arranged in a radiating manner as a whole so as tosandwich the circular no-resistance heating element formed area and thecenter no-resistance heating element formed area.

Incidentally, as illustrated in FIGS. 13, 15, the resistance heatingelement formed on the surface of the ceramic substrate is preferable tobe divided into two or more circuits. Owing to the division of thecircuits, the calorific value can be controlled by electric power to beapplied to the respective circuits and thus, the temperature of theheating face of the silicon wafer can be controlled.

At the time of forming such resistance heating element patterns, in thecase the patterns have wide gaps between neighboring resistance heatingelement patterns as shown in FIG. 15, the resistance heating element caneasily be formed by screen printing. Whereas, in the case the patternshave the narrow gaps and complicated (dense) shape as shown in FIG. 13,by a method comprising steps of at first forming a ring-shaped conductorlayer composed of wide strip-shaped lines and then performing trimmingthe parts (unnecessary parts) where resistance heating element is notsupposed to exist by laser beam, the resistance heating element can berelatively easily formed and therefore advantageous.

In the case of forming the resistance heating element on the surface ofthe ceramic substrate, the thickness of the resistance heating elementis preferably 1 to 30 μm and more preferably 1 to 10 μm. The width ofthe resistance heating element is preferably 0.1 to 20 mm and morepreferably 0.1 to 5 mm.

The resistance value of the resistance heating element can be changed bythe width and the thickness, and the above-mentioned ranges are mostpractical.

The resistance heating element may have a cross-sectional shape witheither a rectangular or an elliptical shape, however it is preferablyflat. It is because if the shape is flat, heat irradiation toward theheating face easily takes place and uneven temperature distribution inthe heating face is hardly caused.

The aspect ratio of the cross-section (width of the resistance heatingelement/thickness of the resistance heating element) is preferably 10 to5000.

It is because the resistance value of the resistance heating element canbe high and the evenness of the temperature in the heating face can beassured as well by controlling the ratio within the range.

In the case of making the thickness of the resistance heating elementconstant, if the aspect ratio is smaller than the above-mentioned range,the transmission quantity of the heat in the heating face direction inthe ceramic substrate is lowered and the temperature distributionsimilar to the patterns of the resistance heating element is caused inthe heating face and on the contrary, the aspect ratio is too high, theportions immediately above the center of the resistance heating elementbecomes at high temperature and consequently, temperature distributionsimilar to the patterns of the resistance heating element is caused inthe heating face. Accordingly, taking the temperature distribution intoconsideration, the aspect ratio of the cross-section is preferably 10 to5000.

Regarding the dispersion of the resistance value of the resistanceheating element, the dispersion of the resistance value in relation tothe average resistance value is preferably 5% or less and morepreferably 1%. The resistance heating element of the present inventionis divided into a plurality of circuits, and keeping the resistancevalue dispersion small as described above makes it possible to decreasethe number of the division of the resistance heating element and makesit easy to control the temperature. Further, the temperature of theheating face during the transition period of temperature rise can becomeeven.

Generally, such a resistance heating element is formed by applying tothe ceramic substrate a conductor containing paste containing a metalparticle and a conductive ceramic particle for ensuring the conductivityand firing the paste. The conductor containing paste is not particularlylimited, however those containing resin, a solvent, and a thickeningagent other than the above-mentioned metal particle or the conductiveceramic are preferable.

As the above-mentioned metal particle, for example, a noble metal (gold,silver, platinum, palladium), lead, tungsten, molybdenum, nickel and thelike are preferable. They may be used alone or in combination of two ormore of them. Because these metals are relatively hard to be oxidizedand have sufficient resistance value enough to generate heat.

As the above-mentioned conductive ceramic, for example, carbide oftungsten and molybdenum can be exemplified. They may be used alone or incombination of two or more of them.

The particle diameter of the metal particle or the conductive ceramicparticle is preferably 1 to 100 μm. It is because if it is too small,less than 1 μm, the surface roughness Ra of the resistance heatingelement easily becomes less than 0.01 μm and at the time of performingtrimming by laser beam irradiation, laser beam is easy to be reflectedand gutters cannot be formed as designed and on the other hand, if theparticle diameter of the metal particle and the like exceeds 100 μm,sintering becomes hard to be carried out to result in a high resistancevalue.

The shape of the above-mentioned metal particle may be spherical orscaly, however it is more preferably spherical. It is because thesurface roughness of the resistance heating element can be more easilyroughened. Further, even in the case of scaly shape, if the aspect ratio(the width or length/the thickness) is not so high, the surfaceroughness can be made high because the particle is disposed easilyperpendicularly or slantingly in relation to the formation face of theresistance heating element.

In the case of using such a metal particle, a mixture of theabove-mentioned spherical particle and the above-mentioned scalyparticle can be used.

In the case the above-mentioned metal particle is a spherical one or amixture of the spherical one and the scaly one, the metal oxide caneasily be held among the metal particle and the adhesion strengthbetween the resistance heating element and the nitride ceramic and thelike can be assured and the resistance value can be high and thereforethey are advantageous.

Further, in the case of an ascicular particle, if it has an aspect ratio(the length in relation to the diameter) not so high, the particle isdisposed easily perpendicularly or slantingly in relation to the formedface of the resistance heating element, so that the surface roughnesscan be high.

As the resin to be used for the conductor containing paste, for example,epoxy resin, phenol resin and the like can be exemplified. Also, as thesolvent, for example, isopropyl alcohol and the like can be exemplified.As the thickening agent, cellulose and the like can be exemplified.

As the conductor containing paste, one containing a metal particle addedwith a metal oxide is used and it is preferable to sinter the metalparticle and the metal oxide after application to the ceramic substrate.Because sintering of the metal oxide together with the metal particlemakes the adhesion of the metal particle and the nitride ceramic of theceramic substrate further close.

The reason for the improvement of the adhesion to the nitride ceramicand the like owing to the metal oxide addition is not made clear,however it can be supposed that the metal particle surface and thesurface of the nitride ceramic and the like are slightly oxidized andcovered with an oxide film and the respective oxide films are unitedlysintered through the metal oxide to cause close adhesion between themetal particle and the nitride ceramic. Further, in the case the ceramicof the ceramic substrate is an oxide, since the surface is naturally theoxide, a conductor layer with a high adhesion strength can be formed.

As the above-mentioned metal oxide, for example, at least one oxideselected from a group consisting of lead oxide, zinc oxide, silica,boron oxide (B₂O₃), alumina, yttria, and titania is preferable to beused.

It is because these oxides can improve the adhesion strength to themetal particle and the nitride ceramic without increasing the resistancevalue of the resistance heating element 112.

The ratio of the above-mentioned lead oxide, zinc oxide, silica, boronoxide (B₂O₃), alumina, yttria, and titania is respectively 1 to 10 forlead oxide, 1 to 30 for silica, 5 to 50 for boron oxide, 20 to 70 forzinc oxide, 1 to 10 for alumina, 1 to 50 for yttria, 1 to 50 for titaniaby weight ratio in the case the total amount of the metal oxides is setto be 100 parts by weight and they are preferable to be adjusted so asto keep their total not exceeding 100 parts by weight.

Adjustment of the quantities of these oxides in these ranges isefficient to improve the adhesion property especially to the nitrideceramic.

The addition amount of the above-mentioned metal oxides in relation tothe metal particle is preferably not less than 0.1% by weight and lessthan 10% by weight. Further, the area resistivity in the case theresistance heating element 12 is formed using such a conductorcontaining paste is preferably 1 to 45 mΩ/□.

If the area resistivity exceeds 45 mΩ/□, the calorific value for theapplied voltage becomes too high and in the case of a ceramic substrate11 bearing the resistance heating element 12 on the surface, thecalorific value becomes difficult to be controlled. If the additionamount of the metal oxides is 10% by weight or more, the arearesistivity exceeds 50 mΩ/□ and the calorific value becomes too high tocontrol the temperature and consequently, the evenness of thetemperature distribution deteriorates.

Further, if necessary, the area resistivity can be controlled to be 50mΩ/□ to 10 Ω/□. If the area resistivity is increased, the pattern widthcan be wide and there occurs no disconnection problem.

In the case the resistance heating element is formed on the surface ofthe ceramic substrate, a metal covering layer is preferable to be formedon the surface part of the resistance heating element. It is because theresistance value change owing to oxidation of the metal sintered body inthe inside can be prevented. The thickness of the metal covering layerto be formed is preferably 0.1 to 10 μm. Such a metal covering layer isto be formed after the above-mentioned trimming treatment is performed.

The metal to be used for the metal covering layer formation is notparticularly limited if it is a non-oxidizable metal and practically,for example, gold, silver, palladium, platinum, nickel and the like canbe exemplified. They can be used alone or in combination of two or moreof them. Among them, nickel is preferable.

It is because, for the resistance heating element, terminals for theconnection to an electric power are required to be attached to theresistance heating element through a solder because nickel can preventthermal diffusion of the solder. As the connection terminals, those madeof Kovar can be exemplified.

The ceramic substrate to be used for manufacturing methods of the secondand the third aspect of the present inventions is preferably a diskplate and those with a diameter exceeding 190 mm are preferable. Becausesuch a substrate with a larger diameter has a wider temperaturedispersion on the heating surface.

The thickness of the above-mentioned ceramic substrate is preferably 25mm or less. Because, if the thickness of the above-mentioned ceramicsubstrate exceeds 25 mm, the temperature-following propertydeteriorates.

The thickness is more preferably not exceeding 1.5 mm and 5 mm or less.Because if the thickness is thicker than 5 mm, the heat transmissionbecomes difficult and the heating efficiency tends to deteriorate,whereas if it is 1.5 mm or less, the heat transmitted in the ceramicsubstrate is not sufficiently diffused, so that the temperaturedistribution possibly becomes uneven in the heating face and thestrength of the ceramic substrate is possibly deteriorated and broken.

In the ceramic heater 110 manufactured by the manufacturing methods ofthe second and the third aspect of the present inventions, a ceramic isused as the material of the substrate, however the material of theceramic is not particularly limited and, for example, a nitride ceramic,a carbide ceramic, and an oxide ceramic can be exemplified.

As the material for the ceramic substrate 111, among them preferable arethe nitride ceramic and the carbide ceramic. Because they are excellentin the thermal conduction.

The above-mentioned nitride ceramic includes, for example, aluminumnitride, silicon nitride, boron nitride, titanium nitride, and the like.Also, the above-mentioned carbide ceramic includes silicon carbide,titanium carbide, boron carbide and the like. Further, as theabove-mentioned oxide ceramic, the example thereof include alumina,cordierite, mullite, silica, beryllia and the like. They may be usedalone or in combination of two or more of them.

Among them, the most preferable is aluminum nitride. Because it has thehighest thermal conduction of 180 W/m·K.

However, a material which hardly absorbs laser beam is preferable forthe ceramic substrate 111 and for example, in the case of the aluminumnitride substrate, those having a carbon content of 5000 ppm or less arepreferable.

Further, the surface roughness is preferably made to have Ra of 20 μm orless according to JIS B 0601 by grinding the surface. Because in thecase the surface roughness is high, laser beam is absorbed.

Further, if necessary, a heat resistant ceramic layer may be formedbetween the resistance heating element and the ceramic substrate. Forexample, in the case of a non-oxide type ceramic, an oxide ceramic maybe formed on the surface.

The method for forming the resistance heating element on the surface ofthe ceramic substrate, using the above-mentioned method, includes: amethod for forming the resistance heating element patterns by applying aconductor containing paste in a plane shape (a ring like shape) to agiven area of the ceramic substrate and then performing laser trimmingto form a resistance heating element; and a method for forming aresistance heating element in given patterns by baking a conductorcontaining paste and then performing laser trimming to form a resistanceheating element. Among these method, a method involving steps of bakingthe conductor containing paste on and then forming the resistanceheating element patterns is preferable since peeling of the conductorcontaining paste layer and the like is not caused by laser beamirradiation.

Incidentally, the sintering of metal is sufficient if the metalparticles are melted and adhered to each other and the metal particlesand the ceramic are melted and adhered to each other. Further, theresistance heating element patterns may be formed by forming theconductor layer in given areas by employing a method of such as aplating and a sputtering and then performing laser trimming.

Next, the ceramic heater manufacturing methods of the second and thethird aspect of the present inventions other than the above-mentionedlaser trimming step will be described with reference to FIG. 16.

FIGS. 16(a) to 16(d) shows cross-sectional view schematicallyillustrating some portion of the ceramic heater manufacturing methods ofthe second and the third aspect of the present inventions including thelaser treatment.

(1) Ceramic Substrate Manufacturing Step

After a slurry is produced by mixing a sintering aid such as yttria(Y₂O₃), a compound containing Na and Ca, and a binder based on thenecessity with a ceramic powder of such as aluminum nitride and theslurry is granulated by spray drying method and the like and the granuleis molded by putting it in a die and pressurizing it to be like a plateand the like and obtain a raw formed body (green).

The raw formed body may be produced by layering green sheets formed by adoctor blade method and the like.

Next, if necessary, parts to be through holes 135 into which insertlifter pins 136 are inserted to transport an object to be heated such asa silicon wafer 139 and parts to be bottomed holes in which temperaturemeasurement elements such as thermocouples are buried are formed.

Next, the raw formed body is heated and fired to be sintered so as toproduce a plate-like body of a ceramic. After that, a ceramic substrate111 is manufactured by processing the plate-like body into a given shape(reference to FIG. 16(a)), however the plate-like body may previously beformed into a shape so as to use the plate-like body as it is. Also, theformed body is heated and fired while it is pressurized from upper andlower sides to make it possible to manufacture a pore-free ceramicsubstrate 111. Heating and firing may be carried out at a sinteringtemperature or more and in the case of a nitride ceramic, it is 1000 to2500° C.

Incidentally, in general, the through holes 135 and the bottomed holes(not illustrated) to insert the temperature measurement elements areformed after firing. The through holes 135 and the like can be formed byblast treatment such as a sand blast using SiC particle after surfacegrinding.

(2) Step of Printing Conductor Containing Paste to Ceramic Substrate

A conductor containing paste is generally a fluid with a high viscositycontaining a metal particle, resin and a solvent. The viscosity of theconductor containing paste is preferably 70 to 90 Pa·s. Since if theviscosity of the conductor containing paste is less than 70 Pa·s, theviscosity is too low to produce a paste containing a metal with an evenconcentration and it becomes difficult to form a conductor layer with aneven thickness, whereas if it exceeds 90 Pa·s, the viscosity of thepaste is too high to do the application work easily and also it becomesimpossible to form a conductor layer with an even thickness. In order toform a conductor layer having a roughened face, the viscosity of theconductor containing paste is preferable to be high. Since the metalwith a scaly or acicular shape is easy to become perpendicular orslantingly to the formation face of the resistance heating element.

The conductor containing paste layer 112 m is formed by screen printingby printing the conductor containing paste in a strip shaped or a ringshaped to the entire area where the resistance heating element is to beformed (FIG. 16(b)).

Since the resistance heating element patterns are required to heat thewhole body of the ceramic substrate at an even temperature, the patternsare preferable to be composed of arcs or concentric circles which areformed repeatedly as to draw some portions of concentric circles asshown in FIGS. 13.

Incidentally, other than the above-mentioned method, the conductor layercan be formed by plating and in this case, by carrying out the platingso as to form an acicular plating layer, the resistance heating elementwith a roughened surface can be formed. In such a case, it is preferableto form the acicular plating layer by forming a thin film by anelectroless plating and the like and then carrying out electroplating onthe thin film.

Further, after a thick film plating layer is formed, etching is carriedout to form the roughened surface.

(3) Conductor Containing Paste Firing Step

The conductor containing paste layer printed at the bottom face of theceramic substrate 111 is heated and fired to remove the resin and thesolvent and at the same time to sinter the metal particle and bake theparticle in the bottom face of the ceramic substrate 111 to form theconductor layer with a given width (reference to FIG. 14) and afterthat, trimming treatment by laser as described above is performed toform resistance heating element (reference to FIG. 16).

In this case, the surface roughness of the conductor layer surface canbe adjusted by changing the heating and firing conditions. Thetemperature of heating and firing is preferably 500 to 1000° C. and byfiring at a relatively low temperature, the metal is prevented frommelting to be flattened and the surface roughness Ra of the conductorlayer can be adjusted to be 0.01 μm or more. Nevertheless, if thetemperature is too low, sintering of metal particles is not promoted andthe resistance value of the resistance heating element becomes too high,so that depending on the metal to be used, a proper firing temperaturehas to be selected.

After the conductor containing paste layer of the resistance heatingelement patterns is formed by the above-mentioned screen printing,plating, and sputtering methods, the layer is fired to be the resistanceheating element 112 and the resistance value of the resistance heatingelement can be adjusted by laser trimming.

(4) Metal Covering Layer Formation

As shown in FIG. 14, a metal covering layer 1120 is preferable to beformed on the surface of the resistance heating elements 112. The metalcovering layer 1120 may be formed by electroplating, electrolessplating, sputtering and the like and in consideration of massproductivity, the electroless plating is the most optimum.

(5) Attachment of Terminals and the Like

Terminals (external terminals 133) for connection to an electric powersource are attached to the terminal parts of the patterns of theresistance heating element 112 by a solder (FIG. 16(d)). Further,thermocouples are embedded in the bottomed holes 134 (not illustrated)and sealed with heat resistant resin of such as polyimide to complete aceramic heater.

Incidentally, the ceramic heater manufactured by the manufacturingmethods of the second and the third aspect of the present inventions canbe used as an electrostatic chuck by forming electrostatic electrodes inthe inside of the ceramic substrate and also can be used as a waferprober by forming a chuck top conductor layer on the surface and guardelectrodes and ground electrodes in the inside.

Next, a ceramic heater of the fourth aspect of the present inventionwill be described.

The ceramic heater of the fourth aspect of the present invention is aceramic heater comprising:

a ceramic substrate; and

a resistance heating element formed on a surface of said ceramicsubstrate,

wherein a gutter or a cut is formed at a part of said resistance heatingelement.

In the ceramic heater of the fourth aspect of the present invention, asgutters or cuts formed in the part of the resistance heating element,for example, similar ones to those described in the manufacturingmethods of the ceramic heater of the second aspect of the presentinvention can be listed.

Also in the ceramic heater of the fourth aspect of the presentinvention, the surface roughness Ra of the surface of theabove-mentioned resistance heating element according to JIS B 0601 is0.01 μm or more and its preferable range is as described above.

Also, in the ceramic heater of the fourth aspect of the presentinvention, the above-mentioned resistance heating element is preferableto be covered with an insulating layer and, as the above-mentionedinsulating layer similar ones to the insulating covering of the ceramicheater of the first aspect of the present invention can be listed.

BEST MODE FOR CARRYING OUT THE INVENTION EXAMPLE 1

After a slurry was produced by mixing and kneading 100 parts by weightof an aluminum nitride powder (the average particle diameter of 1.1 μm),4 parts by weight of yttrium oxide (the average particle diameter of 0.4μm), 12 parts by weight of an acrylic resin binder and alcohol, theslurry was sprayed by a spray drying method to produce a granularpowder.

Next, the granular powder was put in a die and molded into a flat shapeto obtain a raw formed body. The raw formed body was hot pressed at atemperature of 1800° C. and a pressure of 200 kg/cm² to obtain aplate-like sintered body of aluminum nitride with a thickness of 3 mm.Next, the sintered body was cut to obtain a ceramic substrate 11(reference to FIG. 11) for a ceramic heater.

Next, the ceramic substrate was bored by drilling-processing to formthrough holes 15 to insert lifter pins 16 for a semiconductor wafer intoand bottomed holes 14 to embed thermocouples therein.

On the ceramic substrate 11 for which the above-mentioned processing wasfinished, for example, a conductor containing paste was printed by ascreen printing method so as to form patterned strip-shaped resistanceheating element 12 as shown in FIG. 1. The conductor containing pasteemployed in this case was Solvest PS 603D (trade name) manufactured byTokuriki Chemical Research Co., Ltd., which was a so-called silver pastecontaining 7.5% by weight of metal oxides consisting of lead oxide, zincoxide, silica, boron oxide, and alumina (5/55/10/25/10 by weight ratioin this order) in relation to the silver. The silver particle had anaverage particle diameter of 4.5 μm and mainly had a scaly shape.

The ceramic substrate 11 bearing the conductor containing paste washeated and fired at 780° C. to sinter silver in the conductor containingpaste and at the same time bake silver in the ceramic substrate. In thiscase, the resistance heating element 12 of the silver sintered body hada thickness of about 10 μm, a width of about 2.4 mm, and the arearesistivity of 5 mΩ/□.

After that, an insulating covering 17 of an oxide type glass materialwas formed on the surface of the resistance heating element 12.

At first, a paste-like mixture was produced by mixing 87 parts by weightof glass powder having a composition comprising PbO: 30% by weight,SiO₂: 50% by weight, B₂O₃: 15% by weight, Al₂O₃: 3% by weight, andCr₂O₃: 2% by weight with 3 parts by weight of a vehicle and 10 parts byweight of a solvent.

Next, using the paste-like mixture, screen printing was carried out soas to cover the surface of the resistance heating element 12 to form alayer of the paste-like mixture. After that, the paste-like mixture wasdried and fixed at 120° C. and fired at 680° C. for 10 minutes in air toform an insulating covering 17 by being melted and adhered to thesurface of the resistance heating element 12 and the ceramic substrate11. After that, the surface of the insulating covering was subjected tosand blast treatment using a SiC powder with an average particlediameter of 10 μm to adjust the surface roughness Ra of the insulatingcovering. At that time, the thickness of the insulating covering 17 was10 μm. However, the insulating covering 17 was not formed in theconnecting portions of the external terminals 133 in both ends ofcircuits comprising the resistance heating element 12. Accordingly, thecovering state in the vicinity of the external terminals was differentfrom the ceramic heater 10 shown in FIG. 2.

Incidentally, at the time of fusion bonding by heating, a methodinvolving preliminary molding in a shape to be fitted with the shape ofthe insulating covering 17 and then putting the preliminarily formedbody on the resistance heating element 12 and heating the formed body,may be employed as well.

Next, a silver-containing lead paste (made by Tanaka Kikinzoku Kogyo K.K.) was printed in the parts of the resistance heating element 12 wherethe external terminals 13 were to be formed to form a solder layer andfurther, external terminals 13 made of Kovar were put on the solderlayer and heated at 420° C. to carry out reflow and the externalterminals 13 were attached to and fixed in the both end parts of theresistance heating element 12.

Incidentally, as shown in FIG. 2, the resistance heating element 12 andthe external terminals 13 were connected and after that, the insulatingcovering 17 might be formed so as to cover the parts of the resistanceheating element 12 where the external terminals 13 were formed.

After that, thermocouples (not illustrated) for controlling thetemperature of the substrate were inserted into the bottomed holes 14 ofthe ceramic substrate to obtain a ceramic heater 10 as shown in FIG. 1and FIG. 2 and the ceramic heater 10 was fitted in a supporting in whicha heat insulating ring made of fluoro resin for fitting the ceramicheater was formed in the upper part to obtain a hot plat unit.

Incidentally, since the resistance heating element had a givenresistance value, when electric power was applied, heat was generateddue to the Joule's heat to heat a semiconductor wafer 19.

Regarding the ceramic heater 10 constituting the hot plate unit, thethermal expansion coefficient of the insulating covering was measuredand evaluation was carried out by the following methods.

Evaluation Methods

(1) Measurement of Surface Roughness Ra of Insulating Covering

Using Therfcom 920A manufactured by Tokyo Seimitsu Co., Ltd., thesurface roughness Ra and Rmax were measured.

(2) Measurement of Surface Resistance (Area Resistivity) of InsulatingCovering Material

Measurement was carried out at a room temperature and D.C. 100 V.

(3) Evaluation of Oxidation Resistance of Resistance Heating Element

Evaluation was carried out by investigating the change of the heaterresistance after aging in 200° C.×1000 hours.

(4) Evaluation of Dispersion of Temperature Rising Time

After a silicon wafer was put on the hot plate unit, the time(temperature rising time) taken to heat the silicon wafer to 200° C. wasmeasured 10 times and the ratio of the quickest temperature rising timeor the slowest temperature rising time in relation to the averagetemperature rising time was calculated by % and the higher absolutevalue calculated by subtraction from 100% was set to be the dispersionof the temperature rise.

(5) Temperature Dropping Time

After the temperature rise was carried out in the conditions of theabove-mentioned (4), a coolant at 25° C. (cooling air) was supplied at0.1 m³/minute and the time (temperature dropping time) taken for coolingto 50° C. was measured and the average value was set to be thetemperature dropping time.

(6) Sulfurization Resistance

The ambient atmosphere containing 15% by volume of H₂S was kept at 75°C. and the ceramic heater was left for 10 days in the ambient atmosphereand the resistance alteration ratio of the resistance heating elementwas measured for the evaluation of the result as the sulfurizationresistance.

(7) Occurrence of Migration

The hot plate unit was heated to 200° C. in 100% humidity, electricpower was applied for 48 hours and the occurrence of metal diffusionamong resistance heating element patterns was measured by a fluorescentx-ray analyzer (EPM-810S manufactured by Shimadzu Corporation).

EXAMPLE 2

A ceramic heater was manufactured in the same manner as Example 1 andsubjected to the evaluation similarly to Example 1, except that in placeof the oxide type glass material, a heat resistant resin material(polyimide resin) was used and the insulating covering 17 was formed andthe roughening treatment was carried out by the following method. Theresults were shown in Table 1.

That is, at first after a solution of a mixture in a paste-like orviscous liquid-like state containing 80% by weight of an aromaticpolyimide powder and 20% by weight of polyamide acid was produced, thesolution of the mixture was selectively applied so as to cover thesurface of the resistance heating element 12 and form a layer of themixture on the surface of the resistance heating element 12.

Next, the formed layer of the mixture was heated at 350° C. and driedand solidified in a continuously firing furnace to carry out meltbonding of the mixture to the surface of the resistance heating element12 and the ceramic substrate 11. After that, the surface of theinsulating covering was subjected to sand blast treatment using analumina powder with an average particle diameter of 1.0 μm to adjust thesurface roughness Ra of the insulating covering 17. In this case, theaverage thickness of the formed insulating covering 17 was 10 μm.

EXAMPLE 3

A ceramic heater was manufactured in the same manner as Example 1 andsubjected to the evaluation similarly to Example 1, except that in placeof the oxide type glass material, a heat resistant resin material(silicone type resin) was used and the insulating covering 17 was formedand the roughening treatment was carried out by the following method.The results were shown in Table 1.

That is, methylphenyl type silicone resin was selectively applied so asto cover the surface of the resistance heating element 12 by a metalmask printing method and the like and heated at 220° C. and dried andsolidified in an oven to carry out melt bonding of the resin to thesurface of the resistance heating element 12 and the ceramic substrate11. At that time, the thickness of the formed insulating covering 17 was15 μm. The surface roughness Ra of the insulating covering 17 wasadjusted by sand blast treatment using an alumina powder with an averageparticle diameter of 1.5 μm.

EXAMPLE 4

In this example, a ceramic heater was manufactured in the same manner asExample 1 and subjected to the evaluation similarly to Example 1, exceptthat the resistance value of the strip-shaped resistance heating elementwas increased and the thickness of the insulating covering comprisingoxide glass was adjusted to be 20 μm. The results were shown in Table 1.

That was because the resistance value was required to be high in thecase of applying voltage of 30 to 300 V to raise the temperature to 200°C. or more. Incidentally, the adjustment of the surface roughness Ra ofthe insulating covering 17 was conducted by sand blast treatment usingan SiC powder with an average particle diameter of 0.1 μm.

As the paste for the resistance heating element, a paste containingsilver: 56.6% by weight, palladium: 10.3% by weight, SiO₂: 1.1% byweight, B₂O₃: 2.5% by weight, ZnO: 5.6% by weight, PbO: 0.6% by weight,RuO₂: 2.1% by weight, a resin binder 3.4% by weight, and a solvent:17.9% by weight was used.

The resistance heating element patterns had a thickness of 10 μm, awidth of 2.4 mm, and an area resistivity of 150 mΩ/□.

EXAMPLE 5

A ceramic heater was manufactured in the same manner as Example 4 andsubjected to the evaluation similarly to Example 4, except that in placeof the oxide type glass material, a heat resistant resin material(polyimide resin) was used and the insulating covering 17 was formed andthe roughening treatment was carried out by the method as described inExample 2. The thickness of the insulating covering was adjusted to 10μm and the surface roughness Ra of the insulating covering 17 wasadjusted by sand blast treatment using an alumina powder with an averageparticle diameter of 0.1 μm. The results were shown in Table 1.

EXAMPLE 6

A ceramic heater was manufactured in the same manner as Example 4 andsubjected to the evaluation similarly to Example 4, except that in placeof the oxide type glass material, a heat resistant resin material(silicone type resin) was used and the insulating covering 17 was formedand the roughening treatment was carried out by the method as describedin Example 3. The thickness of the insulating covering was adjusted to10 μm and the surface roughness Ra of the insulating covering 17 wasadjusted by sand blast treatment using an alumina powder with an averageparticle diameter of 0.03 μm. The results were shown in Table 1.

COMPARATIVE EXAMPLE 1

A ceramic heater was manufactured in the same manner as Example 1 andsubjected to the evaluation similarly to Example 1, except that theceramic substrate bearing the resistance heating element thereon wasimmersed in an electroless nickel plating bath to form a metal layer ofnickel with a thickness of about 1 μm on the surface of the resistanceheating element. The results were shown in Table 1.

The concentrations of the respective components of the above-mentionednickel plating bath were nickel sulfate 80 g/l, sodium hypophosphite 24g/l, sodium acetate 12 g/l, boric acid 8 g/l, and ammonium chloride 6g/l.

COMPARATIVE EXAMPLE 2

A ceramic heater was manufactured in the same manner as Example 1 andsubjected to the evaluation similarly to Example 1, except that nosurface roughening treatment was carried out after the insulatingcovering was formed on the surface of the resistance heating element 12.Incidentally, the surface roughness Ra of the ceramic heater was 0.07μm. The results were shown in Table 1.

COMPARATIVE EXAMPLE 3

A ceramic heater was manufactured in the same manner as Example 4 andsubjected to the evaluation similarly to Example 1, except that sandblast treatment using a SiC powder with an average particle diameter of15 μm was carried out after the insulating covering was formed on thesurface of the resistance heating element 12 to form an insulatingcovering with a surface roughness Ra of 11 μm. The results were shown inTable 1.

COMPARATIVE EXAMPLE 4

A ceramic heater was manufactured in the same manner as Example 1 andsubjected to the evaluation similarly to Example 1, except that noinsulating covering was formed on the surface of the resistance heatingelement 12. The results were shown in Table 1.

TABLE 1 Surface Thermal roughness Ra expansion Area Oxidation Dispersionof coefficient resistivity resistance of Temperature insulating of of(resistivity temperature dropping Sulfur- covering insulating insulatingchange in rising time time (from ization Insulating covering Ra (μm)covering covering 200° C. × 1000 Hr) (from 25 to 200 to 150° C. resis-Type Composition Rmax (μm) (ppm/° C.) (Ω/□) (%) 200° C.) (%) (second)tance (%) Example 1 Oxide glass PbO—SiO₂— Ra = 0.861 5 10¹⁶ 0.2 0.1 1100 B₂O₃ Rmax = 11.3 Example 2 Polyimide Aromatic type Ra = 0.868 12 10¹⁵0.3 0.2 120 0 resin Rmax = 6.775 Example 3 Silicone type Methylphenyl Ra= 1.009 13 10¹⁵ 0.3 0.1 130 0 resin type Rmax = 6.74 Example 4 Oxideglass PbO—SiO₂— Ra = 0.097 5 10¹⁶ 0.1 0.1 110 0 B₂O₃ Rmax = 1.00 Example5 Polyimide Aromatic Ra = 0.086 12 10¹⁵ 0.3 0.2 130 0 resin type Rmax =1.02 Example 6 Silicone Methylphenyl Ra = 0.022 13 10¹⁵ 0.3 0.4 120 0type resin type Rmax = 1.23 Comparative Plate Nickel — 13.3 50 m 3 0.190 0 Example 1 Comparative Oxide glass PbO—SiO₂— Ra = 0.007 5 10¹⁶ 0.20.5 160 0 Example 2 B₂O₃ Comparative Oxide glass PbO—SiO₂— Ra = 11 510¹⁶ 0.2 0.5 180 0 Example 3 B₂O₃ Comparative — — — — — 20 0.5 90 200Example 4

As being made clear from the results shown in Table 1, in Examples 1 to6, the resistance change of the resistance heating element was as smallas 0.1 to 0.3%, whereas in Comparative Example 1, it was high, that is3%. The reason for that was attributed to resistance alteration owing tothe oxidation of the nickel plating film itself and other than that, itwas supposed that the nickel plating film was porous, thus diffusion ofoxygen and oxidization of the silver occurs in the inside. Further, inExamples 1 to 6, the dispersion of the temperature rising time was smalland the temperature dropping speed was relatively quick, whereas inComparative Examples 2, 3, since the surface roughness Ra of theinsulating covering covering the resistance heating element was too lowor too high, the temperature dropping speed was retarded.

Further, regarding the occurrence of migration, in the ceramic heateraccording to Comparative Example 4, Ag migration took place andoccurrence of short-circuit among the resistance heating elementpatterns was highly probable.

FIG. 6 to FIG. 10 respectively show the graphs showing the measurementresults of the surface roughness of the insulating coveringsconstituting the ceramic heaters according to Examples 1 to 5.

Further, in the ceramic heaters according to Examples 1 and 4, thethermal expansion coefficient of the oxide glass, the insulatingcovering, was 5 ppm/° C. and it was approximately numerically similar tothat of aluminum nitride, 3.5 to 4 ppm/° C. and consequently, theresistance change caused by separation of metal particles constitutingthe resistance heating element owing to expansion and contraction causedin cooling and heating cycles was relatively small as compared with thatin the case of using the heat resistant resin.

In Examples 4 to 6, as the resistance heating element, those having anarea resistivity of 150 mΩ/□ were used. In this case, since the arearesistivity of the insulating covering was 10¹⁵ to 10¹⁶ Ω/□, which isalmost complete insulator, even if voltage of 50 to 200 V was applied,the electric current was transmitted in the inside of the resistanceheating element and the calorific value was also increased, whereas inthe case of forming a nickel plating film as Comparative Example 1, thearea resistivity of the nickel plating film was 50 mΩ/□, smaller thanthat of the resistance heating element, and since electric current istransmitted in parts having a lower resistance value, electric currentwas transmitted through the nickel plating film to result in lowcalorific value.

EXAMPLE 7

A ceramic substrate 21 for a ceramic heater was manufactured in the samemanner as Example 1 and parts to be through holes 25 to insert lifterpins 16 for a semiconductor wafer into and to be bottomed holes 24 toembed thermocouples therein were bored by drilling process.

Next, in the bottom face of the ceramic substrate 21 for which theabove-mentioned processing was finished, the resistance heating elementpatterns 22 a to 22 f with a shape shown in FIG. 3 were formed using thesame material as Example 1.

After that, as shown in FIG. 3, at the resistance heating elementpatterns 22 a, 22 b, and 22 c, the insulating coverings 27 a, 27 b, and27 c of an oxide glass material were formed to cover the areassandwiched by resistance heating element constituting circuits and thestretch of the periphery thereof. And on the other hand, at theresistance heating element patterns 22 d, 22 e, and 22 f, the insulatingcovering 27 d comprising the same material is formed to cover the areassandwiched by resistance heating element patterns constituting circuitsand their peripheral area and entire area among the respective circuits.

The composition of the above-mentioned oxide glass material was the sameas in the case of Example 1, the formation method of the insulatingcovering 27 was same as that of Example 1 except that the covering areaswere extended in a wide area as described above. In this case, thethickness of the insulating covering 27 was 30 μm. However, the portionsof both ends of the circuits to be connected with external terminalswere not covered with the insulating covering 27. The surface roughnessRa of the insulating covering 27 was adjusted by sand blast treatmentusing a SiC powder with an average particle diameter of 5 μm.

After that, thermocouples (not illustrated) for temperature control wereembedded in the bottomed holes 24 of the ceramic substrate to obtain theceramic heater 20 shown in FIG. 3 and FIG. 4.

As described above, after the ceramic heater 20 was manufactured usingthe aluminum nitride substrate 21, evaluation was carried out similarlyto Example 1. The results were shown in Table 2.

EXAMPLE 8

A ceramic heater was manufactured in the same manner as Example 7 andsubjected to the evaluation similarly to Example 7, except that in placeof the oxide type glass material, a heat resistant resin material(polyimide resin) was used and the insulating covering 27 was formed andthe roughening treatment was carried out by the following method. Theresults were shown in Table 2.

That is, at first after a solution of a mixture in a paste-like orviscous liquid-like state containing 80% by weight of an aromaticpolyimide powder and 20% by weight of polyamide acid was produced, thesolution of the mixture was selectively applied so as to cover thesimilar areas to those of Example 7 and heated at 350° C. and dried andsolidified in a continuously firing furnace to form the insulatingcoverings 27 a to 27 d. The thickness of the insulating covering 27 was30 μm and the surface roughness Ra of the insulating covering 27 wasadjusted by sand blast treatment using an alumina powder with an averageparticle diameter of 4.2 μm.

EXAMPLE 9

A ceramic heater was manufactured in the same manner as Example 7 andsubjected to the evaluation similarly to Example 7, except that in placeof the oxide type glass material, a heat resistant resin material(silicone type resin) was used and the insulating covering 27 was formedand the roughening treatment was carried out by the following method.The results were shown in Table 2.

That is, methylphenyl type silicone resin was selectively applied so asto cover the surface of the resistance heating element 12 by a metalmask printing method and the like and heated at 220° C. and dried andsolidified to form the insulating coverings 27 a to 27 d. The thicknessof the insulating covering 27 was 30 μm. The surface roughness Ra of theinsulating covering 27 was adjusted by sand blast treatment using analumina powder with an average particle diameter of 2.0 μm.

TABLE 2 Surface Thermal roughness Ra expansion Sheet OxidationDispersion of coefficient resistivity resistance of Temperatureinsulating of of (resistivity temperature dropping Sulfur- coveringinsulating insulating change in rising time time (from izationInsulating covering Ra (μm) covering covering 200° C. × 1000 Hr) (from25 to 200 to 150° C. resis- Type Composition Rmax (μm) (ppm/° C.) (Ω/□)(%) 200° C.) (%) (second) tance (%) Example 7 Oxide PbO—SiO₂— Ra = 4.0305 10¹⁶ 0.2 0.1 110 0 glass B₂O₃ Rmax = 20.52 Example 8 PolyimideAromatic type Ra = 3.250 12 10¹⁵ 0.3 0.1 120 0 resin Rmax = 20.92Example 9 Silicone Methylphenyl Ra = 2.040 13 10¹⁵ 0.3 0.1 130 0 typetype Rmax = 15.30 resin

As being made clear from the results shown in Table 2, also in Examples7 to 9, the area resistivity of the insulating coverings was as high as10¹⁵ to 10¹⁶ Ω/□ and the resistance change of the resistance heatingelement covered with such insulating coverings was as small as 0.2 to0.3%. Further, the dispersion of the temperature rising time was smalland the temperature dropping speed was relatively quick.

Further, after the oxidation resistant test was carried out in Examples8, 9, the insulating covering 27 was forcibly peeled off from thesurface of the ceramic substrate and observation for checking whethermigration of a metal such as silver on the surface of the resistanceheating element took place or not, was carried out in the same manner asExample 1. As a result, no migration was found taking place.

EXAMPLE 10

A composition containing 100 parts by weight of a SiC powder (averageparticle diameter: 1.1 μm), 4 parts by weight of B₄C, 12 parts by weightof an acrylic binder, and alcohol was spray dried to produce a granularpowder.

Next, the granular powder was put in a die and molded into a flat shapeto obtain a raw formed body and the raw formed body was hot pressed at atemperature of 1890° C. and a pressure of 20 MPa to obtain a plate-likesintered body of SiC with a thickness of about 3 mm. Next, the surfaceof the plate-like sintered body was ground by diamond wheel of #800 andgrinded with a diamond paste to adjust to: Ra=0.008 μm. Further, a glasspaste (G-5177 made by Shouei Chemical Products Inc.) was applied andheated to 600° C. to form a SiO₂ layer with a thickness of 3 μm.

Then, the plate-like sintered body was cut to obtain a disk-like bodywith a diameter of 210 mm as a ceramic substrate. After that, the facewhere the above-mentioned SiO₂ layer was formed was used for the facewhere the resistance heating element was to be formed and as shown inFIG. 5, a ceramic heater was produced in the same manner as Example 1,except that the insulating covering (oxide glass) with a thickness of 50μm was formed in the entire areas where the resistance heating elementwas formed and roughened surface was formed by sand blast treatmentusing a SiC powder with an average particle diameter of 10 μm.

As described above, after the ceramic heater was produced using thesubstrate of SiC, evaluation was carried out similarly to Example 1. Theresults were shown in Table 3.

EXAMPLE 11

A ceramic heater was manufactured in the same manner as Example 10 andsubjected to the evaluation similarly to Example 10, except that inplace of the oxide type glass material, a heat resistant resin material(polyimide resin) was used and the insulating covering 37 was formed andthe roughening treatment was carried out by sand blast using an aluminapowder with an average particle diameter of 10 μm. The results wereshown in Table 3.

That is, at first after a solution of a mixture in a paste-like orviscous liquid-like state containing 80% by weight of an aromaticpolyimide powder and 20% by weight of polyamide acid was produced, thesolution of the mixture was applied so as to cover the entire areaswhere the resistance heating element 12 was formed and form a layer ofthe mixture.

After that, the formed layer of the mixture was heated at 350° C. anddried and solidified in a continuously firing furnace to melt themixture and let it adhered to the surface of the resistance heatingelement and the ceramic substrate, and then roughening treatment wascarried out in the above-mentioned conditions. In this case, thethickness of the formed insulating covering was 50 μm.

EXAMPLE 12

A ceramic heater was manufactured in the same manner as Example 10 andsubjected to the evaluation similarly to Example 10, except thatroughening treatment using a SiC powder with an average particlediameter of 8 μm was carried out for the insulating covering (oxideglass). The results were shown in Table 3.

EXAMPLE 13

A ceramic heater was manufactured in the same manner as Example 10 andsubjected to the evaluation similarly to Example 10, except that inplace of the oxide type glass material, a heat resistant resin material(polyimide resin) was used and the insulating covering 37 was formedsimilarly to Example 11 and roughening treatment using an alumina powderwith an average particle diameter of 8 μm was carried out. The resultswere shown in Table 3.

TABLE 3 Surface Thermal roughness Ra expansion Area Oxidation Dispersionof coefficient resistivity resistance of Temperature insulating of of(resistivity temperature dropping Sulfur- covering insulating insulatingchange in rising time time (from ization Insulating covering Ra (μm)covering covering 200° C. × 1000 Hr) (from 25 to 200 to 150° C. resis-Type Composition Rmax (μm) (ppm/° C.) (Ω/□) (%) 200° C.) (%) (second)tance (%) Example Oxide PbO—SiO₂— Ra = 8.230 5 10¹⁶ 0.2 0.4 110 0 10glass B₂O₃ Rmax = 100.01 Example Polyimide Aromatic type Ra = 9.352 1210¹⁵ 0.3 0.5 120 0 11 resin Rmax = 150.32 Example Oxide PbO—SiO₂— Ra =7.252 5 10¹⁶ 0.2 0.4 130 0 13 glass B₂O₃ Rmax = 98.32 Example PolyimideAromatic type Ra = 6.252 12 10¹⁵ 0.3 0.4 120 0 12 resin Rmax = 82.32

As being made clear from the results shown in Table 3, in Examples 10 to13, the resistance change of the resistance heating element was as smallas 0.2 to 0.3%. Further, the dispersion of the temperature rising timewas slightly high as compared with those of Examples 1 to 7, attributedto high surface roughness of the insulating covering, however thetemperature dropping speed was not so much changed and relatively quick.

As described above, the ceramic heater of the first aspect of thepresent invention had a small resistance change ratio, slight dispersionof temperature rising time, a high temperature dropping time, and wasexcellent in temperature controllability. Further, it was excellent inthe corrosion resistance to reactive gas such as O₂ and H₂S in asemiconductor producing device.

Further, since the insulating covering was of an insulator, even if theresistance value of the resistance heating element was increased, noelectric current flowed in the insulating covering and a heater having ausable range of 150° C. or more was able to be obtained.

Also, in the case the oxide glass was used for the insulating covering,since it had excellent adhesion property to the ceramic substrate andhad a small thermal expansion coefficient, cracks were hardly formed andat the same time, the resistance change ratio of the resistance heatingelement was small.

Further, in the case the heat resistant resin was used for theinsulating covering, the insulating covering could be formed at arelatively low temperature.

As described above, the ceramic heater of the first aspect of thepresent invention was the most optimum to be used as a heater for amiddle temperature range from 200 to 400° C. and a high temperaturerange from 400 to 800° C.

EXAMPLE 14 Adjustment of Resistance Value of Resistance Heating Elementby Laser Trimming

(1) A composition containing 100 parts by weight of an aluminum nitridepowder (average particle diameter: 0.6 μm), 4 parts by weight of yttria(average particle diameter: 0.4 μm), 12 parts by weight of an acrylicresin binder, and alcohol was spray dried to produce a granular powder.

(2) Next, the granular powder was put in a die and molded into a flatshape to obtain a raw formed body (a green).

(3) The raw formed body was hot pressed at a temperature of 1800° C. anda pressure of 20 MPa to obtain a plate-like aluminum nitride body with athickness of 3 mm.

Next, the plate-like body was cut to obtain a disk-like body with adiameter of 210 mm and made to be a plate-like body comprising a ceramic(a ceramic substrate 111). The ceramic substrate was subjected todrilling-process to form through holes 135 to insert lifter pins for asilicon wafer into and bottomed holes 134 (the diameter: 1.1 mm; thedepth: 2 mm) to embed thermocouples in.

(4) A conductor containing paste layer was formed on the ceramicsubstrate 111 obtained in the above-mentioned (3) by screen printing.The printed patterns were the patterns as shown in FIG. 3.

As the conductor containing paste, a paste having a compositioncontaining Ag: 48% by weight, Pt: 21% by weight, SiO₂: 1.0% by weight,B₂O₃: 1.2% by weight, ZnO: 4.1% by weight, PbO: 3.4% by weight, ethylacetate: 3.4% by weight, and butyl carbitol: 17.9% by weight wasemployed.

The conductor containing paste was Ag—Pt paste and silver particle(Ag-540 made by Shouei Chemical Products Inc.) had an average particlediameter of 4.5 μm and a scaly shape. The Pt particle (Pd-221 made byShouei Chemical Products Inc.) had an average particle diameter of 6.8μm and a spherical shape.

The viscosity of the conductor containing paste was 80 Pa·s.

(5) Further, after formation of the conductor containing paste layer ofthe heating element patterns, the ceramic substrate 111 was heated andfired at 850° C. for 10 to 20 minutes to sinter Ag and Pt in theconductor containing paste and at the same time bake them on the ceramicsubstrate.

The resistance heating element patterns had as shown in FIG. 13, sevenchannels 112 a to 112 g. The dispersion of the resistance values of thefour channels (the resistance heating element patterns 112 a to 112 d)in the periphery before performing trimming was 7.4 to 12.4%.

Incidentally, the term, channel, means a circuit to be controlled solelyby applying same voltage and in this example, denotes the respectiveresistance heating element patterns (112 a to 112 g) formed ascontinuous bodies.

The resistance dispersion in the respective channels (the resistanceheating element patterns 112 a to 112 d) was calculated as follows. Thatis, at first, each channel was divided into twenty divisions andresistance thereof was measured between both ends in the divisions.Then, the average value thereof was defined as the average divisionresistance and then, the dispersion was calculated from the differencebetween the highest resistance value and the lowest resistance value andthe average division resistance value. Further, the resistance value inthe respective channels (the resistance heating element patterns 112 ato 112 d) is the total of the resistance values measured separately.

(6) Next, using YAG laser (S143AL, manufactured by NEC, output 5 W,pulse frequency set range 0.1 to 40 kHz) having wavelength of 1060 nm asan equipment for trimming, the pulse frequency was set to be 1.0 kHz.The equipment was equipped with an X-Y stage, a galvanomirror, a CCDcamera, Nd: YAG laser and a controller built therein to control thestage and the galvanomirror, and the controller was connected to acomputer (FC-9821, manufactured by NEC). The computer was provided witha CPU working as a computing unit and a memory unit and also providedwith a hard disk and a 3.5-inch FD drive working as a memory unit and aninput unit.

The resistance heating element pattern data was inputted from the FDdrive to the computer and the position of the resistance heating elementwas read out (reading was carried out on the bases of markers formed inspecified points of the conductor layer or in the ceramic substrate).Then, necessary control data was computed and the resistance heatingelement patterns were irradiated in the direction approximately parallelalong the direction of electric current flow to remove the conductorlayer in the irradiated portions and form gutters with a width of 50 μmreaching the ceramic substrate, so that the resistance value wasadjusted. The resistance heating element had a thickness of 5 μm and awidth of 2.4 mm. The laser was irradiated with a frequency of 1 kHz, anoutput of 0.4 W, a bit size of 10 μm, and a processing speed of 10mm/second.

In such a manner, trimming was performed and the dispersion of theresistance values of four channels (resistance heating element patterns112 a to 112 d) in the periphery after the adjustment of the resistancevalue of the resistance heating element was remarkably decreased to 1.0to 5.0%.

(7) Next, Ni plating was carried out for the portions to which theexternal terminals 133 were to be attached in order to assure theconnection to an electric power, a silver-lead solder paste (made byTanaka Kikinzoku Kogyo K. K.) was printed to form solder layers byscreen printing.

Then, external terminals 133 made of Kovar were put on the solder layersand heated at 420° C. to carry out reflow and the external terminals 133were attached to the surface of the resistance heating element patterns.

(8) Thermocouples for controlling the temperature were sealed withpolyimide to obtain a ceramic heater 110.

EXAMPLE 15 Production of Ceramic Heater (Resistance Heating ElementFormation by Laser Trimming)

In this example, a ceramic heater having the resistance heating elementpatterns shown in FIG. 13 was manufactured.

(1) A composition containing 100 parts by weight of an aluminum nitridepowder (average particle diameter: 1.1 μm), 4 parts by weight of yttria(average particle diameter: 0.4 μm) 12 parts by weight of an acrylicresin binder, and alcohol was spray dried to produce a granular powder.

(2) Next, the granular powder was put in a die and molded into a flatshape to obtain a raw formed body (a green).

(3) The raw formed body was hot pressed at a temperature of 1800° C. anda pressure of 20 MPa to obtain a plate-like aluminum nitride body with athickness of some 3 mm.

Next, the plate-like body was cut to obtain a disk with a diameter of210 mm and made to be a plate-like body made of a ceramic (a ceramicsubstrate 111). The ceramic substrate was subjected to drilling-processto form through holes 135 to insert lifter pins 136 for a silicon waferinto and bottomed holes (not illustrated) (the diameter: 1.1 mm; thedepth: 2 mm) to embed thermocouples in (reference to FIG. 16(a)).

(4) A conductor containing paste layer 112 m was formed on the ceramicsubstrate 111 obtained in the above-mentioned (3) by screen printing.The printed patterns were the concentric circles-like (ring-shaped)patterns having a given width and formed in a plane-shape so as toinclude the resistance heating element patterns 112 a to 112 g which aregoing to be the respective circuits of the resistance heating elementshown 112 in FIG. 13 (reference to FIG. 16(b)).

As the conductor containing paste, a silver paste containing 7.5 partsby weight of metal oxides consisting of lead oxide: 5% by weight, zincoxide: 55% by weight, silica: 10% by weight, boron oxide: 25% by weight,and alumina: 5% by weight in 100 parts by weight of silver was employed.The silver particle (Ag-540, made by Shouei Chemical Products Inc.) hadan average particle diameter of 4.5 μm and a scaly shape.

The viscosity of the conductor containing paste was 80 Pa·s.

(5) Further, after formation of the conductor containing paste layer ofthe heating element patterns, the ceramic substrate 111 was heated andfired at 780° C. for 20 minutes to sinter silver in the conductorcontaining paste and at the same time bake them on the ceramicsubstrate.

(6) Next, using YAG laser (S143AL, manufactured by NEC, output 5 W,pulse frequency set range 0.1 to 40 kHz) having wavelength of 1060 nmwas used as an equipment for trimming, the pulse frequency was set to be1.0 kHz to perform trimming.

The equipment was equipped with an X-Y stage, a galvanomirror, a CCDcamera, Nd: YAG laser and a controller built therein to control thestage and the galvanomirror and the controller was connected to acomputer (FC-9821, manufactured by NEC). The computer was provided witha CPU working as a computing unit and a memory unit and also providedwith a hard disk and a 3.5-inch FD drive working as a memory unit and aninput unit.

The X-Y stage was made to be rotatable at optional angle θ around fixedcenter axis A of the ceramic substrate.

The resistance heating element pattern data was inputted from the FDdrive to the computer and the position of the resistance heating elementwas read out (reading was carried out on the basis of markers formed inspecified points of the conductor layer or in the ceramic substrate) andnecessary control data was computed and while the ceramic substrate 111being rotated, laser beam was irradiated to the portions of theconductor containing paste layer other than the areas where resistanceheating element patterns were to be formed to remove the conductorcontaining paste layer in the irradiated portions and form theresistance heating element 112 with patterns shown in FIG. 13 (referenceto FIG. 16(c)). The resistance heating element had a thickness of 5 μm,a width of 2.4 mm, and an area resistivity of 7.7 mΩ/□.

(7) Next, the ceramic substrate 111 produced in the above-mentioned (6)was immersed in an electroless nickel plating bath of an aqueoussolution containing nickel sulfate 80 g/l, sodium hypophosphite 24 g/l,sodium acetate 12 g/l, boric acid 8 g/l, and ammonium chloride 6 g/l toform a metal covering layer (a nickel layer) 1120 with a thickness ofabout 1 μm on the surface of the silver-lead resistance heating element112.

(8) Solder layers were formed on the portions to which the externalterminals 133 were to be attached in order to assure the connection toan electric power by printing a silver-lead solder paste (made by TanakaKikinzoku Kogyo K.K.) by screen printing.

Then, external terminals 133 made of Kovar were put on the solder layersand heated at 420° C. to carry out reflow and the external terminals 133were attached to the surface of the resistance heating element 112 (FIG.16(d)).

(9) Thermocouples for controlling the temperature were sealed withpolyimide to obtain a ceramic heater 110.

EXAMPLE 16 Adjustment of Resistance Value of Resistance Heating Elementby Laser Trimming

A ceramic heater was manufactured in the same manner as Example 14except that in the step (5) of Example 14, surface roughening wascarried out by sand blast treatment using Al₂O₃ (the average particlediameter: 10 μm) after baking the Ag—Pt paste applied to the ceramicsubstrate.

EXAMPLE 17 Adjustment of Resistance Value of Resistance Heating Elementby Laser Trimming

A ceramic heater was manufactured in the same manner as Example 14except that in the step (5) of Example 14, surface roughening wascarried out by sand blast treatment using Al₂O₃ (the average particlediameter: 20 μm) after baking the Ag—Pt paste applied to the ceramicsubstrate.

EXAMPLE 18

A ceramic heater made of silicon carbide was manufactured in the samemanner as Example 14 except that silicon carbide with an averageparticle diameter of 1.0 μm was used in stead of aluminum nitride andthe sintering temperature was set at 1900° C. and further, after a glasspaste containing 50 parts by weight of a glass powder (borosilicateglass) with an average particle diameter of 0.5 μm, 20 parts by weightof ethyl alcohol, and 5 parts by weight of polyethylene glycol wasapplied to the surface of the obtained heater plate, an SiO₂ layer witha thickness of 10 μm was formed on the surface by firing it at 1500° C.for 2 hours and alumina (the average particle diameter: 0.01 μm) wasused for sand-blasting.

EXAMPLE 19

A ceramic heater made of silicon carbide was manufactured in the samemanner as Example 14 except that silicon carbide with an averageparticle diameter of 1.0 μm was used and the sintering temperature wasset at 1900° C. and further after a glass paste (borosilicate glass)containing 50 parts by weight of a glass powder with an average particlediameter of 0.5 μm, 20 parts by weight of ethyl alcohol, and 5 parts byweight of polyethylene glycol was applied to the surface of the obtainedheater plate, an SiO₂ layer with a thickness of 10 μm was formed on thesurface by firing it at 1500° C. for 2 hours and alumina (the averageparticle diameter: 0.01 μm) was used for the sand blasting.

COMPARATIVE EXAMPLE 5 Adjustment of Resistance Value of ResistanceHeating Element by Laser Trimming

A ceramic heater was manufactured in the same manner as Example 14,except that the resistance heating element was formed by using aconductor containing paste having the following composition and heatingand firing the paste.

The conductor containing paste was a Ag—Pt paste with a composition sameas that in Example 14 and the silver particle (Ag-128, made by ShoueiChemical Products Co., Ltd.) had an average particle diameter of 0.6 μmand a spherical shape. The Pt particle (Pd-215, made by Shouei ChemicalProducts Co., Ltd.) had an average particle diameter of 0.6 μm and aspherical shape.

The viscosity of the conductor containing paste was 80 Pa·s.

Further, after the conductor containing paste layer in the heatingelement patterns was formed, the ceramic substrate 111 was heated andfired at 850° C. for 20 minutes to sinter Ag and Pt in the conductorcontaining paste and bake them on the ceramic substrate 111.

COMPARATIVE EXAMPLE 6 Manufacture of Ceramic Heater (Resistance HeatingElement Formation by Laser Trimming)

A ceramic heater was manufactured in the same manner as Example 15except that the resistance heating element was formed by using aconductor containing paste having the following composition and heatingand firing the paste.

The conductor containing paste was a silver paste with a compositionsame as that in Example 15. The silver particle (Ag-128, made by ShoueiChemical Products Co., Ltd.) had an average particle diameter of 0.6 μmand a spherical shape.

The viscosity of the conductor containing paste was 80 Pa·s.

Further, after the conductor containing paste layer in the resistanceheating element patterns was formed, the ceramic substrate 111 washeated and fired at 780° C. for 20 minutes to sinter silver and lead inthe conductor containing paste and bake them on the ceramic substrate111.

Evaluation Method

(1) Measurement of Surface Roughness Ra of Conductor Layer (ResistanceHeating Element)

The surface roughness Ra of the surface of the resistance heatingelement (the conductor layer) on the ceramic substrate formed in each ofthe above-mentioned Examples and Comparative Examples was measuredaccording to JIS B 0601 using a surface roughness measurement apparatus(Therfcom 920A manufactured by Tokyo Seimitsu Co., Ltd.). The surfaceroughness Ra obtained from the measurement results was shown in Table 1.The charts showing the measurement results of Example 14 and Example 15were respectively shown in FIG. 17 and FIG. 18.

(2) Measurement of Gutter Shape

In Examples 14, 16, 17 and Comparative Example 5, after the resistanceheating element was formed on the ceramic substrate and gutters wereformed on the resistance heating element, the width and the depth of thegutters were measured. Further, in Example 15 and Comparative Example 6,after the conductor layer was formed on the ceramic substrate, gutterswere formed in the portions of the conductor layer to be removed and thewidth and the depth of the gutters were measured. The width and thedepth of the gutters were measured by a laser displacement metermanufactured by Kience Co. The results were shown in Table 4.

(3) Temperature Measurement of Heating Face

After the ceramic heater according to each of the above-mentionedExamples and Comparative Examples was heated to 300° C., the temperatureof the heating face of the ceramic substrate was measured by athermoviewer (IR-162012-0012, manufactured by Nippon Datam Co.) and thetemperature difference between the lowest temperature and the highesttemperature was calculated. The results were shown in Table 4. Thetemperature difference in Table 4 means the temperature differencebetween the lowest temperature and the highest temperature.

(4) Occurrence of Crack Formation

Regarding each ceramic heater of Examples 14 to 19 and ComparativeExamples 5, 6, a glass layer with a thickness of 10 μm was formed byapplying a glass paste (borosilicate glass) comprising 50 parts byweight of a glass powder with an average particle diameter of 0.5 μm, 20parts by weight of ethyl alcohol, and 5 parts by weight of polyethyleneglycol to the surface and firing the paste at 1500° C.

The resulting ceramic heater was heated to 200° C. in an oven andimmersed in water at 25° C. in order to observe the occurrence of thecracks in the glass layer.

For the ceramic heaters of Examples 14 to 18, no crack was observed.However, for the ceramic heaters of Example 19 and Comparative Examples5 and 6, cracks were found formed.

TABLE 4 Surface roughness Ra of conductor Temperature layer (resistanceShape of gutters (μm) difference of heating element) Width Depth heatingface (μm) (dispersion) (dispersion) (° C.) Example 0.8 50 (0.5) 5 (0.05)0.5 14 Example 0.3 50 (0.5) 5 (0.05) 0.5 15 Example 9.8 50 (0.1) 5(0.01) 0.5 16 Example 15 50 (0.1) 5 (0.02) 0.6 17 Example 0.01 50 (0.5)5 (0.05) 0.6 18 Example 18 50 (1.0) 5 (0.1) 1.5 19 Compara- 0.007 50(5.0) 5 (2.0) 5.0 tive Example 5 Compara- 0.005 50 (4.8) 5 (1.9) 4.8tive Example 6

As being made clear from the results shown in Table 4, in ceramicheaters according to Examples 14 to 19, gutters were formed in theresistance heating elements by irradiating laser beam to the resistanceheating elements having a surface roughness Ra of 0.01 μm or more andperforming trimming, and the formed gutters had a width of 50 μm and adepth of 5.0 μm as designed. Accordingly, the resistance values of theresistance heating elements could precisely be adjusted and thetemperature difference between the highest temperature and the lowesttemperature in the heating faces of the ceramic substrate was small.

In Example 15, the resistance heating element was formed by performingtrimming and since the trimming was carried out by irradiating laserbeam to the conductor layer with a surface roughness Ra of 0.01 μm ormore, precise patterns were formed and the temperature differencebetween the highest temperature and the lowest temperature in theheating face was small.

On the other hand, in the case of the ceramic heater according toComparative Example 5, the surface roughness Ra of the resistanceheating element was less than 0.01 μm and the surface was so flat thatthe laser beam was reflected, and gutters could not be formed byperforming trimming, and the resistance value of the resistance heatingelement could not be controlled, and the temperature difference betweenthe highest temperature and the lowest temperature in the heating faceof the ceramic substrate was too large for practical use.

Also, in the case of the ceramic heater according to Comparative Example6, since the surface roughness Ra of the resistance heating element wasless than 0.01 μm, the surface was so flat that the laser beam wasreflected, and gutters could not be formed by performing trimming, andthe resistance heating element with designed patterns could not beformed, and portions of conductor layer which should be removed wereleft and consequently, the temperature difference between the highesttemperature and the lowest temperature in the heating face of theceramic substrate became too large.

Among the ceramic heaters according to Examples, the ceramic heateraccording to Example 19 had the largest temperature difference betweenthe highest temperature and the lowest temperature in the heating face.It was supposed to be attributed to the fact that the surface roughnesswas so high to make the dispersion of the resistance value of theresistance heating element wide, resulting in the large temperaturedifference.

As described above, in the ceramic heaters obtained in Examples, laserbeam was irradiated to the resistance heating element or the conductorlayer with a surface roughness Ra of 0.01 μm or more to performtrimming, so that incomplete trimming of the resistance heating elementor the conductor layer owing to reflection of the laser beam never tookplace and precise patterns were easily formed and grooves with a precisewidth was able to be formed.

INDUSTRIAL APPLICABILITY

As described above, the ceramic heater according to the first aspect ofthe present invention comprises a resistance heating element with asmall resistance change ratio, has a sufficient temperature rising andtemperature dropping speed and is excellent in temperaturecontrollability. Also, corrosion resistance to the reactive gases in asemiconductor producing device is also excellent and the insulatingcovering is of an insulator, so that the resistance value of theresistance heating element can be made high and the heater can be usedas a heater for a middle temperature or a high temperature use.

Further, in the case the insulating covering is formed in the stretch ofgiven area including the resistance heating element-formed area, theabove-mentioned effects are provided and also migration of metal such assilver can be prevented. Further, since the covering is easy, theformation cost of the insulating covering can be reduced.

According to the ceramic heater manufacturing method of the secondaspect of the present invention, since the resistance value of theresistance heating element is adjusted by irradiating laser beam to theresistance heating element having a surface roughness Ra of 0.01 μm ormore according to JIS B 0601 and performing trimming, reflection oflaser beam can be prevented and the resistance heating element can betrimmed as designed and consequently, the resistance value of theresistance heating element can precisely be adjusted.

Also, according to the ceramic heater manufacturing method of the thirdaspect of the present invention, since the resistance heating element ingiven patterns is formed by irradiating laser beam to the conductorlayer having a surface roughness Ra of 0.01 μm or more based on JIS B0601 and performing trimming, reflection of laser beam can be preventedand the unnecessary portions of the conductor layer can be trimmed asdesigned and consequently, a ceramic heater having precise patterns andexcellent in the temperature evenness of the heating face can beobtained.

Further, according to the ceramic heater of the fourth aspect of thepresent invention, since the surface roughness of the resistance heatingelement surface is high, the atmosphere gas can be stagnated and air canbe prevented from flowing in the gutters and the cuts in the resistanceheating element to suppress formation of low temperature portions owingto the existence of the cuts and gutters. Consequently, the temperatureevenness of the heating face can be improved further.

1. A ceramic heater comprising: a ceramic substrate; a resistanceheating element, which is composed of one circuit or more circuits,disposed on a surface of a ceramic substrate; and an insulating coveringprovided on said resistance heating element, wherein said insulatingcovering has a surface roughness Ra of 0.01 to 10 μm in accordance withJIS B
 0601. 2. The ceramic heater according to claim 1, wherein saidinsulating covering is formed in a stretch of area containing a portionon which said circuits are formed.
 3. The ceramic heater according toclaim 1, wherein said ceramic substrate comprises a nitride ceramic or acarbide ceramic.
 4. The ceramic heater according to claim 1, whereinsaid insulating covering comprises an oxide glass.
 5. The ceramic heateraccording to claim 1, wherein said insulating covering comprises a heatresistant resin material.
 6. The ceramic heater according to claim 5,wherein said heat resistant resin material is one kind or more selectedfrom a polymide type resin and a silicone type resin.
 7. The ceramicheater according to claim 1, wherein a heating face is a side opposed tothe side on which said resistance heating element is formed.
 8. Theceramic heater according to claim 1, wherein said insulating coveringcovers the resistance heating element comprising two or more circuits ina lump.
 9. A ceramic heater comprising: a ceramic substrate; and aresistance heating element formed on a surface of said ceramicsubstrate, wherein an elongated gutter or cut is formed at a part ofsaid resistance heating element, and said resistance heating element hasa surface roughness Ra of 0.01 μm or more.
 10. The ceramic heateraccording to claim 9, wherein said resistance heating element is coveredwith an insulating layer.
 11. The ceramic heater according to claim 9,wherein said surface roughness is in accordance with JIS B
 0601. 12. Theceramic heater according to claim 9, wherein said elongated gutter orcut is an elongated gutter that extends substantially parallel to anelectric flow direction of said resistance heating element.
 13. Theceramic heater according to claim 9, wherein said elongated gutter orcut is an elongated cut that extends substantially perpendicular to anelectric flow direction of said resistance heating element.
 14. Theceramic heater according to claim 1, wherein said surface roughness ofsaid insulating covering is provided on an outermost surface of saidceramic heater.
 15. A ceramic heater comprising: a ceramic substrate; aresistance heating element disposed on a surface of said ceramicsubstrate; and an insulating covering provided on said resistanceheating element, wherein said insulating covering has an exteriorsurface with a surface roughness of 0.01 to 10μm.
 16. The ceramic heateraccording to claim 15, wherein said ceramic substrate comprises anitride ceramic or a carbide ceramic.
 17. The ceramic heater accordingto claim 15, wherein said insulating covering comprises an oxide glassor a heat resistant resin material.
 18. The ceramic heater according toclaim 15, wherein said heat resistant resin material is one kind or moreselected from a polymide type resin and a silicone type resin.
 19. Theceramic heater according to claim 15, wherein a heating face is a sideopposed to the side on which said resistance heating element is formed.20. The ceramic heater according to claim 15, wherein said insulatingcovering covers the resistance heating element comprising two or morecircuits in a lump.
 21. The ceramic heater according to claim 15,wherein said surface roughness of said insulating covering is providedon an outermost surface of said ceramic heater.